Kotlin Tutorial For Beginners 2023

What is going on guys. Assalamualaikum. Welcome to Amigoscode in this kotlin crash course I'm going to teach  you pretty much everything you need to get up and running with kotlin. kotlin it's a powerful  and elegant programming language for the jvm and if you're looking to switch from java to  kotlin then this is also the course for you also kotlin now is the main programming  language for Android applications so Android backend and with multi-platform functionality  as well kotlin is a great choice this video is about five hours long and you can find  the timestamps and the description of this video in case you want to navigate to a  particular section before we start this crash course literally just take one second  and smash the like button also if you haven't subscribed do so and without further Ado  let's go ahead and learn about kotlin before we dive into kotlin I just want to say  a few things the first thing that I want to say is that this course is part of the massive  course which I'm currently recording and then planning for kotlin developers and in general  for anyone really that wants to learn quote there now the course is not ready yet so what I want  you to do is join the waiting list and also on the website you can basically enroll get a  certificate but also there's a form that you can find at the end of the course so that  you can give me some suggestions of what are the things that you want to learn about  kotlin so enroll now on the website so that you can stay up to date with the latest  recordings and future updates but more important you'll be eligible for an early  bird discount once the entire course is out let's begin our journey in terms of learning  kotlin kotlin is a concise cross-platform and yet fun it takes all the good things of java and  it adds even more features to make it somewhat a better language kotlin is multi-platform allowing  you to share code for different platforms you can write server-side code so if you're familiar  with the jvm you can run your kotlin code on jvm making it easy for Java developers to switch  to kotlin also you can create multi-platform libraries that works across several platforms and  is the official language for Android development in this page right here you can see that so if  I scroll down they've got a simple example of how to get up and running with kotlin but we'll  go through this later in this course and here as I said kotlin basically allows you to write code  which runs on different platforms so server side Android iOS desktop and web which is like amazing  okay so in this page here we can then basically click on this button to get started with kotlin  so also in this page you can basically click on docs and you can go through this page to learn  about kotlin but hopefully I'm going to break it down for you in this course next let's  go ahead and get up and running with kotlin in order for us to get up and running  with kotlin we've got two options we can use the IDE which I'll show you in a  second so IntelliJ IDEA or Android Studio or if you want to quickly see how cotton is  like you can use the kotlin online editor so here let me just click on it and in here we  can basically write some kotlin code so you can see that this is the version 1.8.21 and in  here you can switch the platform so most of the times you're going to use jvm but you can see  all these different options and in here we can also run the code that you see in here so we'll  go through this in a second but if I run this you can see that we have hello world if I cancel  this and then say hello and then Amigos code and let's just add this into a variable so VAR and  then here I'm going to say brand and then colon and then string equals to and in here just say  Amigos code so we'll go through the syntax in a second but we can take this brand in here and then  just add it in here so basically we are printing the variable if I run this you can see that we  have Amigos code in here so this is basically the playground that allows you to write and basically  try kotlin without you having to install anything next let's install IntelliJ and get  up and running with kotlin for real cool for this course what we're going to use is  the best IDE for the jvm this includes Java and kotlin and by far IntelliJ is the IDE for I  would say serious Engineers okay if you're using Eclipse then it's time for you to switch  and give this IDE a try because it's the best for overall software development so in here  we can click on download and in here you can see that we can download IntelliJ IDEA for  Windows Mac OS as well as Linux and if you are on Intel or apple silicon there's also  the corresponding platform available for you so we have ultimate as well as Community Edition  and the difference between these two is that the ultimate edition gives you profiling tools support  for spring HTTP client JavaScript typescript so basically the whole front-end check bank database  tools remote development which is currently in beta as I speak and also collaborative development  which is not available within the IntelliJ IDEA Community now luckily for you I do have a code  that you can use so that you can get IntelliJ IDEA ultimate for three months yes three months  so if you are taking this course on the website you should find the instructions on how to get the  access code so that you can enjoy this amazing IDE cool now in order for us to download this IDE  we're not going to do through this button in here because the best way for you to manage all  of your ideas is by using something called so if I go to developer tools navigate to where is  it toolbox app so this right here is basically a way for you to manage all of your Ides you can  upgrade have the settings and also you can have different versions running at the same time and  also previews and whatnot so download this toolbox app in here is absolutely for free and get the DMG  or the executable if you're on Windows and once you have it installed in here you should see that  there's this box icon in here so if I click on it you see that this is the jetbrains toolbox now  at this point you can install whatever IDE you see here but the one that we are interested  is the IntelliJ IDEA ultimate so the Community Edition as well you can install it for free  but I'm going to give you the coupon code so that you can try this IDE here for three months  and if I scroll down you can see that we have stuff for python data sea lion dot net in here  so you can basically just install and then just try these Ides and they are so awesome cool so  once you have two books go ahead and click on install so for you you should see installing  here and install IntelliJ IDEA ultimate okie dokie so upon installation of IntelliJ IDEA  also I forgot to mention that you can click on this clock in here and basically you can create  an account and if you manage to get the coupon you should actually create an account and then  log in and basically you should be on your way to getting the three months for free so in here  let me just click on IntelliJ IDEA ultimate and this is basically the latest  version as I speak for IntelliJ IDEA you might see that maybe at some point when you  install IntelliJ you have the new UI and then don't you worry because now I'll show you also  how to switch so this is IntelliJ so here we can basically customize IntelliJ add some plugins and  whatnot which we're not going to do at this point but what we want to do is to create a brand new  project and in here you can see that we can choose have a look so we've got different options in here  so have a look we've got so if I show you we have Maven we have spring we have Java effects quarkos  ktor which I will cover at some point as well kotlin multi-platform view write AWS and whatnot  so what we want to do for us is let's just create in here a new project so just say new project and  then for the name I'm just going to say kotlin in here and I could also create a git repository  and this will allow me to basically push all the examples so that you have it for reference so  I'm going to take this and then for the language you can choose Java kotlin groovy JavaScript  so what we want is kotlin and then the build system in here we're not going to do anything  with Maven or Gradle so just leave IntelliJ and if you want you can add sample code so just  leave it as it is and there's no need for us to configure the advanced settings so just leave  everything as is and one thing that I actually need to do is I need to change the path so here  I'm going to put this under code and not reviews and now advanced settings should reflect on  that okay so choose whatever location that you want to store your project and also we have  here jdk so I'm using the 17 version but what you can do is if you don't have anything in  here just basically set your jdk so click on download jdk and you can see version 20 but at  some point you might see 21 22 23 so it doesn't really matter right so just choose the latest if  you want but in my case I'm going to leave it at 17. but if I want the latest version for example  just leave 20 and then you can choose the vendor in here so either use Oracle or eclipse in  here so let's just say eclipse and for the architecture I'm going to use this one because  I'm on the Mac I think it's M2 Chip and select that one if you're on Intel just use this one here  so eclipse and then download and you can see that now it has installed and we're good to go so as I  said the version doesn't really matter and this is pretty much it so let's add sample code and let's  create just give it a second and that uh we have successfully created a project using kotlin and  now just to make sure that things are working you see display button in here just click  on this play button or in here so just run and if this works it means that we have  everything working properly and you can see that we have Hello World program arguments  and then exit code and then zero which means that there were no issues awesome this is  pretty much it catch me on the next one okay as I said IntelliJ they have a brand new  version of their IDE and basically they have changed the complete look and feel so let's  go ahead and switch to that so maybe by the time you watch this video that will be the default but  currently it's in beta mode so let's just click on this clock in here project IDE and project  settings and then here we can click on settings cool at this point under appearance and behavior  you should see new UI and then beta so here I'm going to enable this and then apply and  restart perfect and now you can see that the UI looks much much better and we'll go through  some of these things in a second but this is pretty much it so I just want to make sure  that we actually switch to the new UI moving forward so that we get the best experience  this all for now catch me in the next one foreign and some of the things that you see here on  the screen because moving forward it's very important that you understand what is going on  so if I open a project in here so you see that we have kotlin so this is our folder which is under  kotlin this is some good stuff and don't worry if it's green in here that's because I didn't  commit none of this and here if I click on SRC Main and then kotlin you should see that so here  I actually have an extra toggle but you should see main.kt which is this file right here so if I  put this smaller which is this file in here okay now this is where we type our kotlin code and if  we want to run it we could just click on this play button or this one or we can right click on  the main and then run right so provided that it has this main function then we're able to  run it so if I change this from Main to Mains in here you see that I'm no longer able to run  this because every kotlin code needs the main function so this is the main entry point for  the application okay so if I put that back you can see that we have the play button and we can  basically run this and whatever is inside the main function will be executed also what I do have  for you is in here so line number four if I press command and then y you can see that you have the  keyboard shortcut so that you can follow along so both for Mac as well as Linux and windows  so basically if I press command Z you can see that command Z and do delete line okay and this is  very helpful so with kotlin code We have basically functions so we'll come back to functions in a  second but just bear in mind that this is the main function and it's the main entry point of  your application within your IDE you can do a bunch of things which we're not going to have  time to cover all the features about the IDE but in a nutshell so this here is the project and  this is where you see all of your files in here and here this is all the git stuff integration  you can see the structure of your file you can see AWS toolkit so for you you might not see this  unless you have the plugin installed also you have Services we have build if you want to use the  integrated terminal you can do it so just click on it and this opens up the terminal in here  and problems you can see all the problems that you currently have within your code and also git  in here so you have get in here and also you can commit through here so this gives you the history  basically so if I click on it you can see what we have so this is currently the master branch  which I'm gonna have to change to main later on but this is pretty much it so here if I hide this  and most of the time what I'm going to do is I'm going to have a separate file for all the examples  so you should see here for example when you talk about variables I'll create a new file in here  called variables.kt so KT is the extension and then I'm going to commit all of these files so  that you have four reference but most of the time I'm going to keep my IDE like this full screen so  that you see everything nice big and bold also if you want to access settings you can click on  this login here and you can go to the project structure go to settings plugins if you want to  change the theme in here so quite useful if I click on theme you can choose between light what  is this what is this don't choose this please or you can choose between the other ones right so oh  this one is quite ugly so please don't you dare choose these themes I think this one is quite good  the default so just use that one and also if you want to have access to the database tool in here  you have access which is really nice but we're not going to touch this later when we touch upon  spring boot so then I might even show you how to use this and finally you have code with me in here  and basically I can invite you to have a Live code session but we're not going to do this as well  and this is pretty much an overview of your IDE a all right let's explore this piece of code which  is the main function and also I'll show you how to use program arguments so basically fun in here  is a reserved keyword for kotlin and then main is the name of this function so unlike Java  so here let me just open project and then let me create a new and then here I'm going to say  Java class and then here I'm going to say main as well so we can have two Mains so this one is  main.java whereas this one is main.kt so here I'm not going to add this to git as of now so let  me just basically don't ask again and then cancel and this is some Java code so if I say in  here so main you don't have to type this but this in contrast is the exact same  thing so if I say South for a second and if I open this main.kt hello world this  is what's inside go back to main.java paste it and now if I put them side by side so I'm just  going to take actually let's just leave the kotlin on top and then take this tab in here and then  put it underneath just like that and then put this full screen and and also what I'm going to do here  is you see line number four and five on main.kt let's get rid of it so I'm just going to select  this line delete or just press command and then y basically this right here is the exact same  thing in Java so have a look so in kotlin you say fun and then Main and you pass some  arguments and then you say print line and in Java is a little bit different  right so here have a look public class Main and then inside you have public static void main  string arcs and then you have system.out.printline and then hello world so you see that it's way  more verbose the Java code when comparing to kotlin in here which is quite simple so it's a fun  Main and then args and then print line so let me just close this in here and basically inside of  this function so inside you can basically type some commands so here print line basically it's  a function it's another function that allows you to print to the console yeah so this when you  run this so let's just click on the Run button or here as well so this will give you so if I  scroll up or just put this bigger have a look hello world and then program arguments so this  prints to the console and inside you can have a string we'll come back to strings in a second  but this is just a series of characters and also in here this is how you basically combine a  string with some type of function or you basically evaluate some variables so this is quite neat  as well whereas Java is a little bit different so in here we just say print hello world and  then we have program arguments so now program arguments these are arguments that you pass when  you run the program so what we can do is so in here within IntelliJ click on these three dots  and then click on configuration and then edit and inside we should see program arguments so here  I'm going to say Foo space bar and then say apply and here we can run and you can see that now we  have hello world program arguments Foo comma bar so full comma bar what is doing this is  this right here okay so I could say args and then get the first element of arcs  by adding square brackets and then zero and if I run the program we should only  have Foo okay so this right here is a utility function that joins the array to  Strings and we will cover arrays in a second and this is pretty much it now obviously we  don't need none of this as we learn kotlin and also this right here so args is optional so we  can get rid of it and this is our main function obviously if we run it we should see  nothing being printed on the console cool so now we have an understanding of the  main function which is pretty much the main entry point for your kotlin program again  if I remove this name in here so if I say X for example or a z I cannot run this okay  so basically I should have one function called Main in order to run whatever is inside this file  cool this is all for now catch me on the next one when writing kotlin code you need to understand  the reserve keywords and these are keywords which are part of the language and cannot be used for  anything else other than writing kotlin code so here you can see they've got a list of hard  keywords of keywords modify keywords and the list in here it's quite extensive in here so field  init param set modifier const data enum and then special characters and then operators mathematical  operators in here equal assignment in here for null safety you can see that basically you've got  these keywords and they cannot be used to combine it do anything else other than writing your kotlin  code okay so let me show you what I mean so if we look into so let's have a look VAR so VAR in here  so declares a mutable property or local variable okay so if I go back to my IDE and inside of my  IDE let me first basically rename this so main.kt I'm going to rename so go to refractor  renamed and then I'm going to call it reserved and then keywords so for each lesson you  should see the corresponding file okay so refactor nothing changes but the file name and  the contents inside are the same so if I say for example VAR in here and then brand equals two  and then here just add double quotes and say for example Amigos code right so this right here is a  reserved keyword and I cannot use it to combine it to for example VAR so instead of the name of the  variable be name brand I cannot say VAR in here right so VAR is used to construct a variable  now the name of this variable which is brand cannot be any of the reserved keywords I  cannot say fun for example because fun is a reserved keyword however I can say main right  so I can give it a name so this is not a reserve keyword I cannot say for example when it's  a reserved keyword I cannot say if I cannot say valve for example so these are Reserve  keywords so I could say name so name is not Reserve keyword and if I want to print the name  in here I can just say name here I can run this and we should see Amigos code now  we have this wiggly line in here and we'll come back to this later but  this is pretty much Reserve keywords let me go ahead and create a brand new file  and their project in here and inside kotlin create a new and then here kotlin class and I'm  going to call this as comments and then in here there's no need for us to have a class so later  we will learn about classes so just have a file press enter and now we have the comments.kt  and you will have access to this as well right so the idea is for every single topic  that we cover we should have the file in here for the corresponding topic now if I  want to have the main function I can say fun and then main right so basically you can have  as many main functions provided that you will run each file separately right so usually  you would not have too many main functions at least one to run the entire program but for us  because we're learning the programming language I want to have the main function in all of these  files so that I can run each file independently cool so if I Collapse project and you saw that we  did type the main function also what we can do is you can say main so just say Main and here you can  see that you have two options you can choose Main just like that nice and easy or if I type main  or just may and then here we could choose the main function with arguments cool let's just  choose the main function without arguments and here if I say print so print allows us to print  anything to the console I'm going to say hello please comment and then me okay  so have a look if I run this we should see hello please comment me and what  we can do is we can add a comment in kotlin by using the forward slash twice and this basically  doesn't execute this statement so if I run this you can see that now there's nothing on the  console so this is a single line comment but also we can have so if I duplicate  this and let me just say inside here so let's just change this to multi and then line so we can have multi-line comments by basically  adding forward slash and Then star and basically you see that IntelliJ did autocompletion for  me there but basically now I can type anything inside and this is a multi-line comment instead of  a single line comment okay so this is a difference and comments basically they allow you to comment  your code and they don't get executed foreign let me just go back to this print line in here  so it's very important I understand exactly what this is doing right so print line in kotlin here  this is used to print the console so if I run this you can see that we have hello please  comment me so this is from the previous video there we go so hello please comment me  let me just say hello in here for a second I'm just gonna say hello and basically when you  say print line in here you can literally pass anything you can pass a string which you're going  to learn later you can pass numbers you can pass objects you can pass characters literally anything  because there's a variation of this print line method and that's achieved with something called  overloading now you learn later overloading when it comes to methods but in here so if I say hello  and then here I'm going to say how are and then you right it doesn't have to be all in camps so  the beginning of each letter but if I run this what you should see is hello and then how are you  on a new line so Ln pretty much just says print and then give a new line which is equivalent as  so if I say print so there's also print in here so if I run this we should see hello how are you  all in one line and this is because here we just print we don't give a new line and then we print  line and the next print or print line will be on a new line because of this and this right here  is the same as this so basically forward slash and then n so this gives a new line even though  I'm not saying print Ln I'm just saying hello and then new line backslash n if I run this  you can see that we have hello how are you so throughout this course we're going to use print  line quite a lot and also what I want to show you is that print so if I basically press command  and then navigate into it or command B and you can see the keyboard shortcut Down Below in here  so command b or Ctrl B on Windows and essentially what this is calling is system dot out dot print  line and then pass it the message so this right here is what this is Java have a look Java Lang  public final class system cool so internally all it's doing it's calling system.out.printline  that's all for now catch me on the next one let's quickly learn about variables so variables  is pretty much a placeholder where you can pretty much store anything so in here there's  a couple of ways of storing variables so you could say VAR you could say vowel in here  and then there's other ways but for now let me just stick with VAR and then I'll show you  better ways of doing this and I'll explain the difference between VAR and vowel very soon  so if I want to store for example a sequence of characters in here I can basically say VAR  and then give the name of the variable followed by so in here the data type and we'll cover data  types in a second but here let's just say string equals 2 and then double quotes and now I can add  a sequence of characters so here I can say Amigos or let's just say Jamal for example there we  go so now this variable in here called name has the contents of Jamal in here if I want to  store Jamal's age for example I can say VAR h and then here colon and if I say string equals  two and then I want to store for example 18 so this is not valid because with  strings you can only store sequence of characters if you want to store  numbers you can basically say int cool so basically a variable allows you to store  one and only one thing and obviously if you want to store multiple things inside of a variable we  have something called data structures so these are arrays lists sets and all that stuff which we will  cover later but those allows us to store multiple values inside of a single variable cool if we want  to print so the variable we could just say print and then I can say name in here let's also print h  in here so name as well as age and let's run this and you can see that we have Jamal  and then 18. if you want to print both on the same line in here what  you can do is you can basically use dollar sign and then curly brackets twice and  then you can pass a value so you can say name and this actually has to be within double quotes  for this to work just like that so name and then also dollar sign curly bracket and then age and  what this allows you to do is to format the string so here I can say Name colon and then I could  say age and then colon and here you can see how it works cool so if I remove this and in fact let  me just put basically duplicate this and then put age in here and let me just comment this out so  you have it for reference so remember single line comments or we could use multi-line let me just  move these above just like that and if I run this you can see that now we have name and  then Jamal age under one single line and this is the concept of variables so once  you store the variables so think of a variable as a placeholder to store values you can use  it then later throughout your program in our case we just use it to print but here we can  do way more than just printing but we'll cover strings and all the operations that we can do with  variables later next let's learn about data types if you come from java background you will know  that in order for you to create a variable you need to say int and then for example a number  equals two and then basically 10 for example right and this is the driver syntax now in kotlin  we don't have this concept of Primitives in here and pretty much everything is an object so in  order for us to create for example a variable that represents a number we can do it in multiple ways  but let me first show you the exact same syntax that you would have in kotlin to compare with  Java so here you need to say VAR and then number and you can see that there's a number and then say  colon and then here you specify the data type so here this will be an INT and then equals to and  then 19 for example or 10 right so this is the exact same thing but in kotlin so kotlin this is  the syntax and this is the Java syntax okay so let me just collapse this in here and this is how you  define a variable that stores numbers if you want to store bigger numbers you could say VAR and  then here I'm going to say L for long and colon and then the data type in here long just like  this and then equals two and then here I could add you know a very long number and I need to add  the L at the end right so the difference between an integer and a long is the size basically  okay so this here stores bigger numbers so the same with double and Float so if you want to  store decimal numbers you can say VAR I'm going to name the variable as D in here colon and then  double n equals two and then 3.14 or 1 2 or 1 3 right and you've seen that I actually been adding  semicolons and this is because you know used to Java but basically you don't need semicolons in  here my bad and also if you want to store bigger numbers that have decimal you can use floats I'm  going to say f in here and this is float equals to and then 3.14 for example and  then we have to say F at the end if you if you want to store booleans  true or false you can say VAR and then here I'm going to say B and the  data type for this is Boolean equals to true or false okay so these are two possible values  and also if you want to store strings basically a sequence of characters you can say VAR and  then s for string and then here just say string and equals to oops and then here you can say  Amigos code and finally if you want to store in here so single characters you can say VAR and then  C so this is the name of the variable and I'll come back to naming conventions and all of that  good stuff but here we say Char in here equals two and then we can add a single character and we need  to add this within the single quotes and then here we could just say a for example for Amigos code so  this is how you basically store single characters and these are pretty much the basic types that you  will encounter there's other ones so there's like a race which I will leave it for later but in a  nutshell this is how you go about and create so let me just say here end for number so these  are the data types that you're going to use within kotlin and if you have custom data types  which you will learn later so with classes then obviously so actually let me just format things  then obviously this will not be an integer but for example you might have a person type right  so then this will be person but more on that later if you have any questions drop me a  message otherwise catch me on the next one okay there's one type of which I want to talk to  you and that is the any type so you see that if you want to have a variable you can say VAR  and then here you can say number for example colon and then you can basically specify whether  it's an integer whether it's a double or any other data type so here let's just say 10 for example  so the same which shrinks right so if I want to have name for example I say Name colon and then  string n equals two and then Jamila for example so in kotlin there's the any data type and  basically the any data type is the type which basically all of these types come from  so integer string double and long and pretty much any other data type hence the name any which  means that I can change this time to any just like this and also this one just like that and from  this point onwards so let me actually go back so here for example if I try to put a string  inside I'm not allowed right but if I say any in here I can literally put anything I want so here  I could say string I can say number I can say a decimal like that I can add a character like that  so just bear in mind that if you see this it means that this variable right here can basically hold  any data type and if I press command so just press command on your keyboard and go into it and you  can see the keyboard shortcut command b or Ctrl B on Windows and here any so public open class will  cover a public open class as well as package later but here the root of the kotlin class and every  kotlin class has any as a super class so basically this is the root so here let me just close this  and this is pretty much the any data type and just before we wrap up this video you shouldn't really  use this right so you shouldn't have all of your data types as any because it will cause lots of  confusion right so always be specific on the data type if you're using strings just push strings if  you're using integers then put integers right so don't use the any data type for every single  variable out there catch me on the next one so far you've seen that we have VAR and  then the data type long double float Boolean string Char and whatnot so doing  this actually is not needed because we can use a feature called type inference  which means that kotlin will actually determine the type for us without has  having to explicitly Define the type so what we can do is we can get rid of the type  all together so here this can go just like that and even IntelliJ if I put my mouse in here you  can see that explicitly given type is redundant and what it means basically we don't need this so  we can get rid of that so let's get rid of all of those so float as well as Boolean string basically  literally for everything and for characters and you can see that this is much neater so  don't declare the types and obviously there are times when you want to declare the types but  we'll cover that later most of the times just use type inference which allows you to define  the variable without having to define the type all right cool so in here you saw that we  can define a variable by saying for example brand equals two and  then here we can say Amigos code so this is one way of defining the variable  and we can also Define a variable using the Val keyword so this is Val keyword and here we  could just say let me just say B for now equals to and then omega's code okay so let me actually  say brand and then vowel and brand and then VAR just like that cool now what is the difference  between VAR and Val well with VAR basically I can change the contents of the variable once it's  been assigned which means that I can go right so here I can say brand VAR equals to something else  so here I could say code then with Amigos code for example right so this is the difference whereas  with Val so when you define the variable Val you basically cannot perform the exact same  thing so here if I duplicate this line and and bring it down just like that and  then change this from VAR to vowel so vowel in here so I want to  change the contents of brand vowel from Amigos code to something else I cannot and  you can see that it's telling me file cannot be reassigned change to Val instead so basically  this is how to create an immutable variable meaning that once you define it you cannot change  it so in Java this would be the equivalent of so in here so in Java this is final and then string  and then brand equals to and then Amigos code so this is the equivalent in Java okay and  once you assign this you cannot reassign it and this is the difference between brand and  vowel now obviously which one should you choose so technically you should prefer immutability  always because it's easy to reason about changes especially when you are within a multi-threaded  environment but this is more on the advanced stuff so for now I would say use Val and if you  need to reassign the variable change it to VAR okay so JavaScript they have the exact same  concept so JavaScript they've got VAR and const so it's the exact same concept cool this  is pretty much it and let me just comment this because otherwise we'll have an issue this  pretty much it catch me on the next one okey dokey you've seen Val in here so Val let's  just say name equals to and then Jamal and you've seen the VAR I equals two and then zero the  difference is that with Val this is read only and this one is mutable so you can change  the value in here right so if I try to change name to equal something else I cannot but if I do  VAR or actually sorry I equals two and then two for example I can do this All right  so let me just comment this out in here and we also have something called const which  allows us to create values that will never change so the cost keyword is as follows you say const  and then you give it a name now in here if I pretty much just say const and then the value of  pi for example equals 2. so const and then I need to specify whether vowel or VAR so let's just say  vowel in here and the value of pi let's just say 3.14 let's just keep it simple right so basically  in Java this is the same as static and then final this right here is the same as so final basically  this is the same as Final in Java and this is static and then final now obviously if you want to  create a constant you basically have to Define it outside so basically it could not be inside of a  function now you might be saying right so I could actually Define the same thing without vowel right  so what is the difference well the difference is that const vowel so this value is known before  code execution before you even run your code so we know this value in here whereas Val so if I  just say vowel then it's impossible right because I could have so let's just say in here if I say  we're going to you're going to learn this later if I say func and then get and then pi and then  the value and we're going to have parenthesis and here's a colon and let's just Define the type  so this will be double so let's just say double and then equals to 3 0.14 okay don't you worry  too much about this but this is me creating a function that just Returns the value of pi  which is 3.14 now with a constant right here so you see that we have a function and if I was  to say the value of pi in here is get and then Pi this does not work because I'm dependent  on this code to load the actual value so here if I put a mouse in here you can see const  Val initializer should be a constant value whereas if I say vowel and then I'm going to say  Pi in lowercase equals to get and then pi value so this is allowed and if I say const this is  not allowed right so this is the same as the final keyword in Java and this is static Final in  Java so this is how you create constants in Python so it simply means that when you say const  this value must be known before execution so here if I say 3.14 I know the value right  so the value is here and it's not been computed from somewhere else cool hopefully you understand  the difference between const and vowel and VAR and if you have any questions feel free to let  me know otherwise catch me on the next one in this video let me walk you through nulls  with kotlin so here let's say that we have a variable called name and let's just  say Jamila and in Java we can take name and then say equals to and then no now in kotlin  this is not possible so kotlin type system is aimed at eliminating the danger of null references  so it means that if you want to reassign a variable to something null this right here cannot  be no right and this will avoid many issues and in Java this is the issue so no pointer exception so  this guy in here and it's one which is very common to beginners to understand why is it happening  but basically if you have your variable that is null and you try to perform any operation on  a variable which is no then you have the null pointer exception whereas in kotlin this is not  possible which means that you can safely say for example so here if I print and we'll cover strings  in detail later but I can say name Dot and then here you can see that we have a couple of methods  so get compare equals to string in here drop last filter lowercase and whatnot so let's just say for  example uppercase so uppercase so this will take this name in here and transform all characters  to uppercase so if I run this main function you can see that we have Jamila in uppercase  now if you for example want the ability of a variable to be null what you can do is  the following so here let's just say VAR and then brand and then let's define the  type this will be a string and this can be equal to and let's just say Amigos code  and now if I take brand and say equals to no so basically no in here so this is not allowed  and for us to do this we need to add question mark in here so now this variable in here can have  the null value which means basically pointing to nothing so in this case the variable name is  pointing to the string reference called Jamila whereas here it's just pointing to literally  nothing so if we print this value this will be no cool so if I take this actually so let's just  put it null in here and if we say print line and here we're going to pass brand Dot and then  uppercase just like that now immediately you can see that basically it's telling me the value of  brand is always null right so if I try to run this I'm not allowed right so we get compilation error  so what we have to do is just add a question mark so question mark and now it says right so we  know that this can actually be null so in order for us to you know invoke the uppercase on the  variable brand which might be null we need to be sure so it's either going to uppercase or it's  going to print no right so here if I run this and you can see that we get no in here  and this is how kotlin protects us from no pointer exceptions so now here if I was to  say Migos code so we don't get if I run this we don't get no but we get Amigos code instead in  uppercase and we're good to go now there are a couple things that we can do with this syntax in  here but we'll discuss this later when we touch on if statements but for now I just wanted to  teach you the concept of null safety with kotlin okay dokey let's cover the string class in kotlin  which allows you to store a sequence of characters and pretty much if you want to store any text this  is what you should use so let's learn so here if I want to create a string for example I just say  vowel and I can say for example name equals two and we can say Ahmed for example so this is one  way of creating the string or if you want also you can add string just like this and as you saw that  this is redundant okay so let's just remove this now we have this variable called name that stores  this text if I want to print the variable or the string itself I just say print Ln and then in here  we can run and you can see that we have Ahmed in here so which strings we can perform a bunch of  things with it so here if I say dot this gives me the list of all possible methods available to us  so you can see uppercase so you've seen this where you want to turn the entire string to uppercase  so let me just in here duplicate this command D and then say dot and then uppercase in here if  you want this to lowercase you just say lower and then case so you say dot and then uppercase  and then here you invoke the function itself we'll cover functions later but this is how  you turn the string to uppercase as well as lowercase also if you want to know the number of  characters that this string has just say dot and then length so length is actually a property and  not a method available within the string class and we'll cover also properties as well as functions  and methods cool let's explore other methods so if I say print Ln I can say name and basically I can  actually grab the first character of the string by adding so I can add the square brackets in here  and then I can specify an index so 0 means this index in here one two three and then four so if  I duplicate this and then say 4 in here this will give me capital A and this will give me D in here  so if we run this let's just run this for a second and you can see that we have capital a lowercase  D we've got five so Ahmed has five letters in here we turn Ahmed to all uppercase and here  we turn Ahmed to all lowercase so you've got a bunch of these functions in here and the best  way of learning this is basically explore the documentation so if I say name Dot and in here  I can basically navigate and then see whether there's a method that does what I want but this  is kind of it right so you have a bunch of these that you can use so any a sequence for each and  whatnot so it's null or blank so it's not empty so for example here if I say is let's say is empty  right here right so if I say it's empty so we know that this will give this false because there's  something within that string but if I pass an empty string like so so empty string and then I  invoke dot is empty run it this will give me true okay so you've got a bunch of these methods  that you can use within this string class and the way you're going to get used to  these methods is just by using this string class and it's one which you use quite a lot  within any programming language to be honest okay cool the other thing I want to cover is let's  say that you want to in here let's just say that you have a variable so Val and then you have H so  H equals two and then let's just say 20. so here if you want to print two strings together you can  say print in here or in fact let's just add it to so here VAR and then let's just say message equals  two and if you want to combine both the name variable and H into one you could just say name  plus and then here you can concatenate another string to give a space and then plus and then h  so you could do this and if I print the message so this right here will gives us name and then  20 Ahmed now don't do this so this is the old way of doing things and the better way is for  you to use the string template so here just add double quotes and add dollar sign and then  curly brackets and then here you can specify name so the variable itself should go inside  here and also we can have the H so dollar sign oops like that Curly bracket and then H so this  is a better way of doing things now even better what we can do is we can remove the curly  brackets so you can see that the syntax now becomes way shorter and easier to read and  this should be actually vowel not a VAR vowel and you can see that we have the message and  here we're combining both and the cool thing here is that I can say name right and then here  maybe I want to have a comma for example and an H just like that if I run this there we go you see that I have name so this is a  string and then Ahmed this is the value and then comma Space Age and then colon and then 20 in here  so this is how you combine strings and this is the best way of doing so and obviously this data type  here is actually string so here if I say colon and then string it returns a string and we can  perform all the other methods that you've seen the other thing I want to cover is multi-line  strings with kotlin and that is let's say that we have a method in here so let's just say  that we have a variable so Val and an email and then I can say equals and here just add  the quotes once twice and then three times and then press enter so once you press enter this  will be autofilled for you so trim indent and what we can do now inside here we can basically  have so hello how how R and then U okay so we could basically have line one line  two line three line four so on and so forth so if I print let's just print the  email so email in here and then run this have a look so you can see that we have hello  how are you in three different lines right and the cool thing here is that this actually keeps  the indentation for us so if I add you know two spaces in between run it oops not debug it but  run it you can see that we have hello how are you the Oracle thing is if you want to add  for example name so hello and the name you want to pass a name for example into this  string so here you can say percent and then s so which means that you want to pass a  string and now I can say email Dot and then format in here and I can pass the arguments  right so here I can say for example hello and then Anna okay so this will be hello Anna how  are you so if I run this have a look so we have hello Anna how are you now obviously if you want  to pass for example a digit this percent d and you can even format things and I would encourage  you to look into how you can format your strings but this is pretty much the multi-line string  feature within kotlin format right so format doesn't have to be with multi-line so it could  also be within a normal string in here so here if I say dot and you can see that we have format  and you can pass whatever formatting so percent s for example and then that will be replaced as  well awesome this is pretty much what I wanted to cover about strings if you have any questions drop  me a message otherwise catch me on the next one in this video let's learn about how to compare  strings in kotlin so in kotlin we have an extra operator which is the triple equals which we  don't have in Java and it kind of works the exact same way so let me break it down to you so  let's say that we have a variable so here must say Val name one equals two and then Sally so we  have this variable in here called name one and in here let's have another variable so I'm going  to say vowel name and then two equals to Jamila now in here what we're now in here when we want  to compare these two to see whether they are the same we have couple options so you know that this  right here so when we say Val this is a read-only value in here so if you want to reassign this you  are not allowed so if I say name two go name one equals to something else not allowed so if we want  to compare these two values we have to use D so if I say print Ln in here the variable name so name  one and then we can say equals so double equals and then in here we can say name and  then two so if I run this in here you should see that we have false because  in here name one not equal to name two so the contents of name one not equal  to name two now in Java this here so um it wouldn't work right so if you took my Java  course you would have known that this right here is not used for Strings and in kotlin also what we  can do is we can say name one dot and then equals so one variable equals to another variable so if I  run this in here you can see that both of them are returning false now if I create a third variable  so Val and then here I'm going to say name three equals to and then Saleh and let's change  now and here so let's ignore name two and let's change this from name two to name three  and the same in here if we run this what do you think the output if we run this what do you  think the output will be so here if I run this you can see that both of them are returning  true okay now this is actually correct and that's because when we say equals right so  double equals or equals here we are comparing the contents I.E whatever we have inside so if  this was to be lowercase s in here and run this you can see that now both of  them are returning false right cool so this is nice and easy now what about if  I put this back and you know that the equals in here and Dot equals will return true so what about  now if I create the string using this so just say string so this is another way of creating strings  and inside paste Saleh so just like that so Sally just like this and say dot and then two car  array so this is how we create a string using the string construct so this is a Constructor  and you will learn more about Constructors later so now what do you think the output for this  will be well the first one in here so let's just um use some some string template so  double quotes and then I'm going to say double equals and then dollar sign and in  here let's basically print the result of this like that and then end with double quotes and  we'll do the same here so double quotes here and double quotes and then close this  with curly bracket and then dollar sign curly bracket and here we're going to say Dot and  then equals so I want you to see the output now what do you think the output for this will be so  double equals in here versus Dot and then equals so if we run this let's have a look what the  output will be so in here we have true and then true right so here nothing has changed and from  this you know that d double equals as well as dot equals on strings they are comparing the contents  so in Java this right here so equals so 2 equals is comparing the memory location and if you want  to achieve the exact same thing in kotlin what you do is the following so here we pretty much  say so let me just duplicate this in here and we say triple equals in here so now this is actually  comparing the memory location right so inside of the string pool which I'm about to show you if  I run this in here so let's just run this which equal equals have a look this is false right so in  here what we've done is so when I say string and then we pass Sally so this is creating a brand new  object and it's not reusing the contents of sale which is stored within the string pool so if I was  to go back in here so let's just get rid of that in here as well and this right now should give  us true before it give us false but if I run it you can see that we have equals right so they are  the same in terms of the value in terms of the reference and here the value as well and this is  pretty much how you compare strings in kotlin now let me put this back in here so that you have it  for reference but let me explain this in a diagram foreign so what is happening is the following we have  a variable called name one and the value of it is Saleh then we created name two which is  equals to jamida now these when we create them the value for them is stored within the string  pool then when we say name three and then we say string so we basically use the string Constructor  this is creating a brand new object called sale so that's why when we use the triple equals  it's comparing the reference to where they are in memory and obviously you can see that name  three and name one they are in completely two different locations in memory hence the triple  equals returns false but double equals and Dot equals will return true because the contents are  the same so sale and then Sally with capital s and you saw that when we changed it back  so when we changed it from the normal way of creating strings I.E in here so this is  basically how you integrate strings all the time and let me have it for reference in here so  you can see and let me just remove that in here and also two car array or chart whatever you  want to say it and let me just comment this so if we were to create a string like this  right so variable name three equals to sale what's going to happen is name three we'll  basically check whether there is a value for sale within this string pool and if it does  it just points to the exact same location so this is the video of string pull and it's a  special area in memory Just For Strings because strings are the most used data type in kotlin and  pretty much in all programming languages and they are a bit special in terms of how they are stored  so that it increases performance and also that we don't waste memory okay so when we create strings  the normal way it basically checks whether there is something within the string pool if there is  it just points to it if not it will just create in the swing pool and then refer to it but  when you create using the string Constructor it basically creates a brand new object so if you  were to create name four for example in here right so name four and basically if you use the string  so here if you just say like that so Val and then basically name four equals to  and then Sally so if you do this name four will point to Saleh inside of the string  pool just like this right however if you do this in here name four equals to so this is what I've  been saying string and then you put salad inside and then you say two and then car or char Ray  just like that so let me just put this on the side like this so if you do this way then it's not  even going to reuse the exact same solid in here it's going to create a brand new object in here  and then it's just going to point to it like so and you can see that now there's a bunch of waste  sadly here Sally here and Sally here so when it comes to Strings avoid creating strings like  this and always do it this way if you have any questions on equality and string pulls feel free  to let me know otherwise catch me on the next one cool in this video let's learn about the  arithmetic operators that ships with pretty much any programming language and kotlin also is  no different so in here you saw that if you have so here we can have numbers so if I have 10 so  number 10 equals 2 and then vowel and then number let's just say number two equals two and then two  in here so let's just name this as number one and if you want to add these two numbers you can  print so let's just print and we can say number and then one plus and then number two so  this is how you add numbers together so if you want to subtract it's the same thing but  you just say minus if you want to divide you divide like so and if you want to times these  two numbers you just add the star in here so also there's something called the mod so  let me just duplicate this instead and this pretty much is the remainder and this goes like  this so 10 and then mod so the percent sign here and then the number two so ten more two it means  how many times two goes into ten basically so it goes into ten five times and the remainder  is zero if I bring this in display button in here you can see that we have 10 plus 2  is 12 10 minus 2 is 8 and then 10 divided by two is five and then 10 times 2 is 20 and  10 mod 2 is 0. so if I was to change this from three so three goes into ten three times  and the remainder will be one if I run this there we go you see that this time is one and  all the other operations actually change as well and this is pretty much it let me just add some  formatting in here so here we could just actually let me just select this right here and then  Ctrl G couple of times and here I'm going to add double quotes and then this will be dollar  sign and then curly brackets and let's go on the other side and then add parenthesis or actually  double quotes and we're going to finish it like so there we go and then here I'm going  to say add space and here I'm going to say oh actually let's just add this  symbol right so Plus this is minus this is division this is subtraction oh actually  multiplication and this is the modulo so here and if I run this there we go you see that now we have  formatted the output cool obviously you can format this better but because my font is quite big I'm  going to leave it as is and as always because I'm used to Java I just need to remove the semicolons  because it's not needed this is pretty much the arithmetic operators that kotlin comes with and  pretty much this is standard in every language you've seen all of these operators in here  so plus minus division multiplication as well as the module let me actually show you  there's a class called math and basically the way you use it is let me actually show  you the long way so here if I say kotlin so this is a package basically and we learn  about packages later and then have a look math and here I can say dot and I've got access to a  bunch of things so here I've got the value of pi if I want to know the value of pi and you can see  the data type is double there's absolute methods a course a sign probably remember this from  GCSE level seal cosine exponential floor log Max so if you want to know the max between  two numbers this is how you do it right so in here round you can also round a number  so you've got tan and I think that's pretty much it right so let's say that here I want  to know the value of pi so I could just say pi and I can print this so let's just print just  like this and if I run this so here run this guy and there you go so this is the value of pi  in here if I want to know the max between two numbers so I just say Max so this time I could  just say Max instead of the fully qualified name okay so here we can also remove this and we  have we and we have to import properly right so from kotlin and math or dot pipe basically so one  thing to note is so when you do this it actually it adds this import statement at the very top  and we'll cover this later but basically this is just saying right so bring the value of  pi which lives in a different package into this class in here and also the same with Max  right so Max in here so we can say Max and if I press command P it takes two numbers so 10 oh  actually let's just say I think we have number one and also number two right so between these  two numbers I want to know which one is the max so let me just say print and just like that run  this and you can see that 10 is actually the max if you want the Min so let me just remove  this and let me just remove this so oops not like that but let me just get rid of that so I  have space so let's say 10 and 3 I think or two it doesn't matter so if I want Min I just say Min  in here and here it says that it doesn't know Min that's because we need to import Min so you can  use IntelliJ to import the function so just put your mouse in there or you can duplicate this and  say Min in here and it should work if you don't want to import everything so here you can see that  I do have a bunch of imports I could just say star so pretty much just bring everything and I can  get rid of all of this right right here and you can see that some people prefer this some people  don't I personally disagree with this so I like to import whatever I need instead of bringing the  entire world cool so if I want to know the main so here if I run this and we'll cover packages later  so the minimum is three if you want to round so on and so forth so let's just explore one more  method so print line and here I can say kotlin dot and then math Dot and let's have a look  square root S square root right here so square root in here of basically let's have a double  so 5.0 sorry s q where root sqrt so run this and you can see that it's two point yeah right  so not helpful and if you want to I think round print line and then kotlin Dot and then math and  in here let's just use round so if I want to round so let's just pass a double so 4.2 for example if  I want to round this you can see that this gives us four right so if it's 4.5 so 4.5 in here run  it this gives us four so it always rounds down so I'm gonna leave it here but basically just  bear in mind that this is how you use the math class within kotlin and this is actually not  needed and I just did this to show you the Imports but we'll cover more packages and imports  later this pretty Madrid catch me on the next one since we are working with numbers and let's focus  on the plus plus and minus minus operators so plus plus and minus minus let me just comment  this in here so if we have so let's just say print Ln and then we have a number so  let's just say in here let's just say Val number equals to and then let's just say 10  in here if I want to increment this number by one all I do is I could say plus and then  one right so if I run this file in here you can see that I do have 11 in here if I want  to increment by 2 I could say 2 so on and so forth right but there's a shorthand when you  want to increment just by one and I use it and that is using the plus plus operator in here and  the space in here it's not needed now this here is complaining because when we say number plus  plus remember if it's a vowel it means that we cannot do this so Val it means that we cannot take  number and say equals 2 and then something else right so in our case we want to say 11 okay so if  it's Val we're not allowed to do this but what we want to do is change this to VAR so hopefully now  you understand the differences and if I run this you should see that we have 10 but  why is that right so why is that so in order for me to explain we have two concepts  we also can do number plus plus B4 so plus plus B4 just like that and if I comment this out this  second line for a second and then run this you can see that now we have 11 which is nice  so the difference is so in here plus plus before the number increments and Returns the value so  that's why you see 11. so increments first and then Returns the value whereas with the second one  number plus plus in here this Returns the number and then increments when I mean Returns the  number when it prints out it has the current value so it prints the current value and only then  it increments the number which means that the next time that I print number in here this will be what  have a guess so if I bring this this will be 11. cool so hopefully you understand the difference  now if I was 2 so in here remove this have a guess what this will be so let's go step  by step so print Ln plus plus number so this will be 11 because it increments the number first and  then returns right then in here what this will be so the value now is 11. so this is return  11 and then increment so this will be 11. and in here this will be what 12. cool  let's just check whether we are right and there we go 11 11 and then 12. cool so the  other thing that we can do is so we have plus plus but we also have minus minus so here let me  just duplicate this twice if I say minus minus and let's just say minus minus here and finally let's  print the number in here so in here we have 12 we say minus minus number this basically decrements  and Returns the number so this will be 11. and in here the number is 11 so we're going to  return the number and only then decrement so this will be 11 and then the final number should  be 10. so the original number so if we run this we should see 11 11 and then 10 and this  is pretty much the plus and minus operators if you have any questions on this please let  me know otherwise catch me on the next one cool let me talk to you about the plus  operator because it's very special in a sense that when you are dealing with numbers  it has a completely Behavior to when you are working with strings so you know how to work  with numbers now strings and you've seen all of this now if I say sum equals to 10 plus 10 so  these are two numbers and some string 10 in here plus and then 10. what do you think the value  will be so this one here what do you think this will be what 10 plus 10 is 20 of course but here  10 plus 10. so what this will be if we run this there we go so here have a look  sum on numbers 20 some on strings this is a thousand and ten but this is wrong  right so basically the plus sign in here and this is basically a concept of polymorphism  which means that many forms so the plus sign when applied on numbers it performs addition  when applied on strings it just performs concatenation so you just concatenate in these  two strings together and not performing any arithmetic operation on these two strings so  bear that in mind okay very important concept that many beginners fail to understand but  this is was special about the plus operator and bear in mind that this only applies to plus  so here when dealing with shrinks I cannot say minus right so 10 minus another string right so  here I cannot say times nor divide nor modular right so this only applies to the plus operator  this is pretty much it catch me on the next one cool now let me teach you that if you have let's  say in here we have a number so let's just say number and then equals two and  then 10. so this is a string and I want to print in here let's just say that  we want to print in here 10 and then Plus and then basically the number 10 right and you saw  that this does not work right so when you have a number and you want to work with strings you know  these are two different types and what we can do is we can take number and then convert that into  a number so just say number Dot and then say two and have a look so we have two string two big  decimal big integer to Boolean to byte to chart array to double to end so on and so forth  so you could convert one type to another so say to int and now I've converted this string  right here into an integer so if we run this there we go so now we have 20. so all I want to  show you here is that if you have so if you have let's say 10 in here and you want to I don't  know maybe you want to add it to number 10. so let's just say 10 in here right so this now is  the way around so this is a number and we want to concatenate a number with a string so if I want to  turn this number into a string we can say 10 Dot and then 2 and then here we can say string so 10  and then two straight so I think hold on so 10 Dot and the IDE doesn't really recognize that I'm  within here so I think you have to basically add a space and then basically say dot again or Dot and  then basically press Ctrl space I think this is a bug but if I have in here number or let's just say  vowel number and then two equals to 10 this time so then here I think number two Dot and basically  you have no issues okay so I think I just found a book with IntelliJ so 10 dot it doesn't work have  a look I don't see the order completion but if I press Ctrl space then it works cool so here if  you want to convert a number to a decimal or to a string just say two and then you can see to byte  to end to float to long to string there we go and then I can say plus number and now remember so  string to string this will be a thousand and ten so if you want to convert any number to a  different data type just say dot two so dot so in here let's just take a double for  example so Val let's say d for double equals two three point zero and if I print D  and let's also print D in here I can say dot and then here two have a look to integer  to string to flow to double to Big decimal so to duration as well and whatnot but  here let's just change that to an integer so it will be three instead of 3.0 have a look 3.0  and 3. and just before we end this video IntelliJ is actually telling me that I can replace this  in here with so in here we can replace this so let me just duplicate this line and leave it  here for you so we can replace that with this I've just put my mouse in there now the reason  why I did that so to string is just to show you how to convert from one data time to another  this is pretty much it catch me on the next one in this section let's learn about the constructs  that kotlin has when it comes to conditionals and decision making first let's learn about  the Boolean data type which you've seen before but let me actually go in detail now  so a Boolean is pretty much a data type that allows you to hold true or false values so  here if I was to say for example is and then adult equals 2 and then here I can  say true or I can say false so this is a Boolean okay so is adult this is  false then we can say for example Val is and then male for example equals true right  now here you can see that the possible values are true or false and we'll come back how to use  these values in a second but in a nutshell this is what a Boolean is if I was to print these values  it will just print true or false so if I also say print and then is adult is just going to print  in here if I run this it's going to print false the value right here awesome so this is false nice  and easy now in kotlin everything is an object and this means that also booleans can be null so here  if I say for example Val order and then completed so maybe you want to represent an order right so  ordered complete equals to and let's say that we want to assign the value of no so no means that it  has literally no value assigned to it now in order for us to say that this is actually a Boolean  right here we need to use the data type so here we say Boolean so this is a Boolean and in  order for us to assign this to null we need to say that this actually needs a question  mark and here remember the question mark and this now is a Boolean whose value  is no so booleans can be false true or no I'll come back to when we use these values  and that's basically with if statements and I'll show you the best way of using them especially  when they are null which is really important so here if I was to print the  order completed will just get no here we go so false null and let's also print  the other one which is let me just do it here and this is is and then mail and let me just  pull this up there we go if I run this you can see that we have false true as well as no so  these are the three possible values for booleans cool now that you know the three possible values  for booleans now let me quickly explain the naming convention for booleans so with booleans  you kind of want to always ask a question so instead of saying adult in  here you say is and then adult is male here is so is and then order completed  right here so this is a better name okay so you basically always try to ask a question that  will return true or false for example did you eat did you sleep right so you can also say  for example in here has and then slipped right so it is slept doesn't really make sense but  has slept right or maybe is and then completed as well so all I want you to bear in mind is whenever  you work with booleans so let me just put this right here at the bottom so you always want to  ask a question for the variable name that you are about to create and even with functions as  well right so later you learn about functions so if your function returns a Boolean value then  you always want to ask a question so this makes much sense instead of just saying sleep or slept  or completed okay so is has and basically try and always ask a question when naming your booleans  this is pretty much it catch me on the next one cool let me now talk about logical operators when  dealing with booleans so let's say that in here we have two booleans so Val and then is and then  female for example and here let's just say false so if you want to combine these two booleans in  here so here I'm just going to print but we could also store the result into a variable so if you  want to combine two booleans you say is adult and then you can say and so this is the and operator  and this should be is female so here I'm saying is adult and is female so when you use the and in  here and this is the conjunction or logical and so every single expression in here has to be true  in order for the entire expression so this entire expression to evaluate to true so this has  to be true this also has to be true in order for the output to be true if I run this you can  see that this is false okay and that's because of is female is false so if I was to change  this to true now in here and then run this there we go you see that this is true and we  can actually combine so let me just come back in here we can combine multiple ants so you know just  limited to one and but if you want to have another and and in here you can say true as well right so  let's actually put this into a variable in here so Val and then is and then pilot for example or is  the driver so easy driver equals two and then true so now if I say is driver  in here and if I run this you can see that this is still false and  that's because of this is female so this is the and we also have the disjunction which  is the or so here if I say print line I can say is in an adult or so or so  these two pipes or is female right and or it's also known as a disjunction  so this is the logical or so this basically at least one of them has to be true for this entire  expression to evaluate to true so it's adult in here so this is true then it bails out because  it doesn't really matter or okay so if I run this so this will give this true in here true  so we've got two outputs so the last one is this one and it's true because this  is true then it doesn't need to know whether this is true now if we flip  things around so if we say is female and then or and then is adult it's female this  equals to false then it tries the other value right so or so is this true no all right or  let's try if this is true if this is true then it's going to be true so if we run this this  will be true and if this here is false so if it's idle is false the entire thing will be false  right so at least one of them has to be true and again you can combine multiple oars together  in here to create a more complex expression and the last thing I want to show you  is the negation so negation works as photos so you can take whatever Boolean  you have so if I say is and then adult and you can say is not adult so you basically you  flip the expression so you say exclamation mark and this now when you say is not so this will  basically flip the value if the value is true this will be false if the value is false this  will be true so if I show you so if I run this is adult is true but now it's going to be false  and similarly is female right so here is female so if I want to say if if if I want to say is not  female I just say print line and then not is and then female so this basically flips the value  for us so if I run this this will be true right so it's not female basically all right so this  is pretty much it now obviously also you could use parenthesis so here if you want to combine  let's say line number five if you want to say is adult and so here so and we can combine here  we can combine these two in here with parenthesis and basically this becomes now a sub expression  and at least one of them has to be true right for the entire thing to be true which means that  now have a look is female and is driver this will evaluate to false false and true so false and  true equals to false but if I was to maybe negate this so let me just run this so you see that this  is actually false in here false but if I also say is not a female right so this now becomes true  and this is true as well and basically now the whole expression is true if I run this this  will be true but also what I could do is if I don't flip the value I could say or in here so  you can see how I'm combining multiple logical operators in here so it's female so this is  false or is driver so this entire thing now will be true because this driver is true is adult  true true and true equal to true if I run this there we go have a look true awesome so this  is pretty much how to use the logical operators with kotlin if you have any questions drop me  a message otherwise catch me on the next one cool you've seen logical operators now let  me teach you about comparison operators so comparison operators allows  us to compare two or more values and the result of the comparison is a  Boolean so if we have for example so Val and then let's just say and one for number one  and let's just say that this is 10 Val and two equals to and then 20. what we could do is I'm  just going to say in here Val result equals two if I want to check whether number one is  greater than number two I can say N1 greater then number two so I could just say N2 in here and  if I print the result so print and then the result if I run this you should see that this gives us  false this is a Boolean value so this is false so this expression right here returns true or false  so this is greater if you want less so let's just basically take this and not even store it within  a variable and just put it here so that you have access to it so if you want to check whether it's  greater or equal you just say greater or equal if you want to say whether it's less so so less  you basically flip the value so less and the way that I remember this is basically this sign right  here has a shape of an l so this is less and here this is less or equal and also if you want to  check whether the numbers are equal you could just say n 1 and then double equals so these  are the comparison operators so if we run this you should see that we have a bunch of booleans  right so here so the first one was what the first one was N1 greater than N2 false greater or  equal false is a less yes true less or equal true and then finally is it equal to N2 and  obviously there are two different numbers hence you've got false and this is pretty much how  you compare numbers using the comparison operators this is the machete catch me on the next one okie dokie you've learned about logical operators  you've also learned about comparison and booleans now where they come into play is with if  statements so if statements allows us to execute a piece of code based of a condition  so let's say that we want to execute so we want to say if so this is the if statement so if N1  is greater than N2 so if N1 is greater than N2 in here we want to have a smiley face so print  and then here Ln and let's just have a smiley face just like that so if N1 is greater than  N2 we want to print a smiley face if I run this it doesn't print anything why because N1 in here  is 10 10 is less than 20. hence this right here is false but if also change N1 to 30 right we could  run this and now we have a smiley face so N1 now is bigger than N2 now here obviously we could say  greater or equal we can also have and so we could say and as well right so as you've seen before and  this right here so the entire expression evaluates always to true or false right so if I was to say  that you know n 1 is greater than N2 but also n 1 is less or equal to 30 for example  well this will be true right because N1 and here is greater or equal than N2 30 and  1 is less or equal than 30. so if I run this you can see that we have a smiley face  but if I change this to 31 in here so 31 run this this doesn't print  anything in here right that's because N1 in here it's not less or  equal than 30 it's actually 31. so this code will evaluate if this entire thing is  true you could also say or if you want right so or remember so or and now basically one of them has  to be true so if I run this this time it prints because the first expression is true cool so this  is the if statement also what I want to show you is that if we have so print Ln and then some  code this will always print regardless because it's not within the if statement okay so  if we basically here let's just say and and I want you to see that this is false but some  code will always be executed because it's outside of the if statement okay so any code that you put  inside will evaluate if this expression is true next let's talk about the else statement all right so you saw if statement but what about  if you want some code to be executed when this is false right so basically the default when  this expression in here doesn't evaluate to what you are asking for well for that we  have the else statement so else in here so this will be executed when this expression  doesn't evaluate to what you are looking for so here we want this to be true in here  so if this is true this will be executed otherwise this will always be executed so  let's just take this duplicate bring it down and let's just add a sad face for example  there we go cool so if I run this in here we should see that we have a sad face why  because N1 in here yes is bigger than N2 but it's not less than 30 right so 31 so if we  change this to or let's just change this to an or there we go so this time this should print and the  else will not be printed so let's just run this and you can see that we have the happy face  and some code so some code is always printed and this right here is our if  statement so if else if this is true then execute this and then skip this carry on  if this is false if this is false skip this so the inside and execute this piece of code and then  carry on and this my friends is if else statement now one thing to bear in mind is that so  else it's not needed right so if you don't need the else statement by all means get rid  of it right but if you want something to be executed in the event that the if expression is  false then add D else statement right so this is valid as we've seen before right this  is all for now catch me in the next one all right so you know about the if you know  about the else what about if you want to perform way more conditions before you reach the else  Branch so maybe you want to say if this is true then if you want to try something else something  else something else until you reach this condition well we have the else so else and then if just  like that and in here we add the curly brackets as usual and with this in here we can have an  expression so let's say that we want to say that n is or N1 equals to 100 for example right so we  could do that and then perform something else in here right if we want to check another condition  you could keep on repeating this so else if maybe 200 so on and so forth and you can see  that the general idea is that you have one if as many else IFS and then an optional else in here  so if else if else if and then else and this is pretty much the construct for if statements now  there's something that I want to talk to you and that is that the if it's not really a statement  but it's more an expression let me show you why foreign let me teach you something with kotlin and that  is that if in here so the if statement is not a statement but it's an expression so even though  that I said if statement is so that you can resemble with other languages because Java they  call it as if statement JavaScript golang you call him as if statements right now the reason why they  are called Expressions is because they can return a value so in here let's say that instead of me  printing the value like so so print Ln the happy face or else the sad face what I can do is I can  just remove so actually let me just comment this for now here so I want you to see something  so if I comment this in here so this line and here I can just basically add the  happy face and also here I can add the sad face so what is this doing well this is  basically returning so return the value of this string right here right so the string or  number or anything else so which means that this actually is not needed and by default now this  whole expression so this if expression Returns the value so here I can say Val and then I can  say value equals to so you can see that now I'm storing the value happy face or sad face and I  can print it right here so I can just say print Ln and then the value right so hopefully  now you can see how this is an expression so if I run this main method in here so right  click and then run and you should see that now we have the happy face hooray which is the  same thing that you saw in here right so here uh the beauty of this actually is that you  can basically have any logic so any code in here and whatever comes last is what you return  from this expression okay so here even though so let's just remove that and say true in  here and let's just change this to false right so even though if I run this we should see  true right so true and then the happy face you know here I'm printing here I'm printing but  then whatever comes last is the return value of this expression so this is pretty much why if  is an expression instead of a statement because of this return value awesome so hopefully  you know exactly what are the differences and let me show you the else Branch here  so if we change this to an and in here so basically is greater than N2 and also less  or equal to 30 now this should be false and we get false and the sad face and also this code  which is outside of the if expression always evaluates basically this one in here awesome  this is pretty much it catch me on the next one in Java we have something called the tenery  operator which basically goes like this so if we want to assign a variable to base of the condition where we have only an if  and then an else statement we could say VAR and then result equals to and then the condition  so let's just say that this let's just keep it nice and simple so we say well if N1 is greater  or equal to N2 then we have a value so in our case let's just say the happy face otherwise so  otherwise we have the sad face just like this so this is when you have scenarios with one if  and else and that's it usually if you can have more so if else if but I don't recommend  it to do that so in cases where your if and else in here they are so simple and you're  just returning one value there's not much logic inside literally it's just a value that  you're returning so what you can do instead is so obviously in kotlin these are expressions  right so the if is an expression so what you do is let me just comment this out and duplicate  and comment so in kotlin is like this you say if and then your expression just like that  and then you remove the question mark right here and instead of the colon you just  say else so this is the exact same thing as the tenery in Java right so let me just say  R for result so everything is smaller in here oops are in here so you can see how different  this is right so you just basically use the if as you've seen before if this is the case  this is true this is the value otherwise sad face right so if also print in here let  me just say V for Value instead actually so if I was to print so print Ln  and then V so let's just run this there we go we've got happy face if and one in  here so N1 is less than N2 let's just say 19. and then run we get the sad face now obviously  we can expand this right here so maybe you want to have another else if in here so what do you do  well we can let me just put this on a new line but basically we could so I'm going to duplicate  this and this could be Val actually vowel and in Java there's no Valdez VAR so if you want  to have else if inside of this expression what you do is the following so let me just duplicate this  and this I'm going to call it V and then one and let's just put this on a new line and then here on  a new line and what we could do is we could say in between if and then else in here the expression so  let's just say that n is equal to 100 for example N1 then we give the value so the value would  be hooray and this should be else if I bet so in here else if and there we go so you can see  how this is clean and beautiful code right and you can combine multiple of these right here but I'll  just leave it with one so if you want a second one for example just duplicate this line and you could  add 200 for example array and then 200. something like that right and now you can see that if  you just returning one value you could just use light detonatory operator in Java but way  more improved catch me on the next one foreign let's look into the when expression with kotlin  so in Java we have the switch so switch statement where we can switch upon a value so we say value  in here and within that switch statement we have cases and within cases then we have to say break  and within that then we can basically return a value or we could just perform something right now  in kotlin what we have is the when statement so it can be used as a statement or as an expression  so in here let's say that we have Val and let's just represent gender in here and let's just  say f for female okay now we can say when and the value so we can say gender  in here so when and then here we can Define the possible outcomes so here  say F so basically if the value is f then have this Arrow so minus sign and then  the greater sign and then here we can print so let's just print female if it's a male so  if it's m in here we can basically say print and then mail and we also have the default so  we can say else in here and within the else statement we also need the error and inside  we can say print and then unknown known and then gender for example just like this now if  we run this what we should get is female right so because if this is equal to f with print line  female if M we print mail otherwise unknown so if I was to say for example this this is  not a valid gender so it says unknown gender cool so this right here is the when statement  this can also be used as an expression meaning that we can return a value from it so if you want  to store the actual so here let me just say Val and then I'm going to give it a name so G let's  just say G for gender and then I can say equals to and from now on this now is an expression because  this now returns so it returns a value so we can get rid of the print lines all together just  like that so in here we get rid of all of that and now the value of G contains female male or  gender in here so if I print so let's just print line and then G in here and let's just change  this to input and then I'm going to say input and this will be gender so much  better and now if we print gender so you can see that we store that inside of  a variable unknown gender if we pass in here M and in here you can see that we have male and  this is pretty much the gist of the when statement so use when when you have multiple branches and  it's very similar to the switch statement in Java cool and always remember so if it returns a  value it's an expression otherwise if you want to return a value from it it's just a statement  this is pretty much hit catch me on the next one cool let me go over a few other things that  you can do with the one expression you saw that in here we have the if else if else if  and then else statement so what you can do is you can actually replace all of this with  the when expression so if you want to replace this with one expression you do basically  when and basically you add nothing inside in here and you basically have your  conditions right so here this we take this and then come back paste it here and we need  parenthesis and add the error and then you can perform whatever you want so in our case  what did you do yeah so we just printed this right here like so and you can  see that now we've switched that from and if else to the when so similarly if you want  to have a second case you can have the second case like so so here it doesn't really matter  so n and then equals to 200 or 100 for example then you can do whatever so print and then Foo  right and then at the end we also have the else and basically oops not like that but I have the  error and basically here we can print and then the sand face so obviously you can repeat this as many  times you want and you can see that you go from if to when which is kinda neat right then the  other thing that we can also do so let me just add a comment here so if else to when expression  so the other thing is so we'll talk about ranges later but if we have for example a value and let's  just say h and let's say that H in here equals to 18. so what we can do is we can say right so when  and then here this time we're going to pass h and we're going to say right so if age is in and then  some range right so if H is in between let's say 13 and then dot dot and 19 for example in here if  this is the case right we can execute something so we can say print Ln and then teenager teenager  right and we can keep on combining these right so it will check the first one and then if you  want you can negate this you can say not in and then you can provide a range right so zero  for example to all the way to 12 for example then you can do something right so print line for  example or if you want you can also have the else in here and you can perform something within  the color brackets or if you just want to print for example you could just do it but you see  that this when statement is actually way more powerful than we thought cool so I'm going to  leave it here for the when statement and as we go through our joining template of learning  kotlin you will see the when expression in action but just remember that it's very powerful  this is pretty much it catch me on the next one cool early on you've learned about the Boolean  and what it is and you saw that also that with booleans you have three possible values so  you can have a Boolean so here if I say Val and then let's just say is and then adult  and then here I can say equals to false true or if I want this to be nullable in here this  is possible right now obviously when it comes to performing these checks whether the Boolean is  equal to true or not so more often so what you do is you'd say if and then is adult in here and  you can see that this right here it says that oops sorry so basically we need to actually add equals  equals to true but I'll explain this in a second so if this is false in here this works if this  is true this also works but when you have your Boolean as null in here it is necessary for us  to perform so if your Boolean can be no in here so if we say right so the data type of this is  and then Boolean right so if we say that this in here can be no so what we need to do is we need  to perform the actual checks so if it's equals to true in here and you know in Java for example this  is redundant where you just have if and then your actual Boolean but in kotlin if it's now this is  the way to do it if equals equals true that means that the value itself is not null and is true  otherwise so otherwise in here so if I say else so in here I can say print line and I can say  false or no so here let me just say print line and I'm going to say not null and true so if I run  this in here so let's just run this you should see that we have in a second force or no there we go  false or no if I change this to let's say true so this now is irrelevant so let's just run this you should see that not null and true right  which is true and as I said if you know that for a fact that your Boolean will never be  no no need for that and also this check here is redundant if adult equals equals to true  this can just be that okay but really what I wanted to teach you is the fact that when  booleans are no you have to perform this check in this session let's learn about arrays and lists  so far you've seen that if you want to store a value for example a string you can basically say  VAR name or vowel in here and basically you can Define the type or not so this is the string and  this allows us to store a sequence of characters but the issue is that this variable right here  called name can only store the evalued Jamila what about if you want to store for example  Jamila you want to store for example jams or maybe some other value now obviously  we can do this under a string but this is not the right approach so in this section let's  learn how to properly work with arrays and lists and also later we'll learn the constructs that  allows us to iterate through arrays and lists awesome catch me on the next one foreign let us first understand a race and then we'll look  into lists which is a better implementation of arrays so if I want to store the value Jamila and  Jamis under a data type that allows us to store multiple values we're going to use arrays so here  what I'm going to do is let me just comment this for now so I'm going to comment this like so and  what we're going to do is I'm going to say Val in here and then instead of name  I'm going to say names equals to and at this point we can use the array of so  this right here allows us to create an array and when we say array of here we can pass  the values so here I'm going to say Jamila and let's also say jammies for example now this  here is slightly different than this string because here we have the first value and then  here we have the second value whereas here we only have one value which is separated by a comma  and this is the construct of creating an array now we can also Define the type for our array  in here and this has to do with generics which will kind of cover later but for now let's  just keep things as is but essentially in a nutshell if for example so here let me  just put this on a new line just like that so if I was to have for example here number two  you can see that my array accepts number two now if I want to prevent this from happening I  can basically say array of and then here I can Define the type so have the less sign and greater  sign and then here we can specify the data type that we only want this array to store so in our  case strings if you want integers you can say int if you want doubles you can say double right  so here if we say string number two in here you can see that we have a compilation error  so we cannot store number two in here and if we only have strings you can see that this becomes  redundant and we can get rid of it just like that cool now if I was to print so let's  just print names in here right click run you can see that we have this random string  in here and by default if you want to print an array you have to do a little bit more work  and then right after names you can say dot content to and then string so this is a  method function and we'll cover these later but if I run this you should see that now we  have Jamila and then Jammers in here now one thing to bear in mind with arrays is that  these are stored in what's called indexes so this is the first index so this right here is  the zero index one index and so on and so forth so if I for example wanted to get hold of  the first index I would say in here print and then names and then square brackets zero so  the zero index corresponds to Jamila in here then the one index in here so one index corresponds  to jammers if I was to have for example Sami in here so this would be index number two so  if I basically duplicate that index number two run and you can see that we have Jamila Jammers  and then Sami what about if I try to access so if I try to access index number and then  three for example so index number three so here if I run this we should get an error and  the error is in here array out of bound so array index out of bound exception because basically  there's nothing at index 3 which is empty cool so let me just basically comment this  out in here and these are arrays in a nutshell now obviously if you want to change for  example Jamila in here so if you want to change the name of Jamila right so here you  can say names and then the index which is zero and here I can say equals 2 and then a different  name so let's say Samira for example so this now will print Jamila and the names zero Samira will  replace the content of the first index in here and if I run this you can see that initially  it was Jamila but then we change it to Samira cool also in here if I hide this if you  wanted to know for example the size of how many elements you have you can basically in  here it's just right at the end we can say print Ln and then names Dot and then size so  this will give us the number of size if I print we should have three inside have  a look three elements inside and if I was to remove and if I was to add one more  we would get four so on and so forth also one other thing that I want to show you  is if I want to check whether so let's just say whether a particular name is within the  array so we could for example use if in here and then we could have the string that we're  looking for so here let's just say hello and then we can say in names so if  this is the case I'm going to say print and then found for example otherwise not found there we go not and then found so if I was to  run this we should get not found have a look not found but if I for example try and search for  jammers in here so Jammers is Jammers in names you can see that it's found so this is  one way that we can use the in keyword to check whether something exists  within the array and one last thing that I want to emphasize with  arrays is that once you define the array itself you are no longer able to  resize so the size of this array right here it's three and cannot be expanded nor shrinked  cool next let's continue to explore arrays cool so you've seen how to work  with the Rays you've seen indexes you've seen size also you've seen  the in keyword or the in operator and also how to print the array to string  because otherwise you get a funny character also what I want to quickly show you is that  this is one of many ways of creating a race so if I scroll down in here and let's basically  add a comment like that so in here if I say array so you can see that we have a bunch of constructs  for array of so you've seen this array of nulls so this will initialize an array of so let's say that  we want to store strings for example and then we also have to pass the size how many elements  that we want to store in here and this right here so array of nulls so let me just put this  on a new line like that so the array now in here contains five spaces and all of them are  no so if I show you so if I say print Ln array of nulls Dot and remember the method  content to string so if we just run this you can see that we have no no no no no no  no now obviously you've seen that if I want to change so array of nulls and then here let's  just change the position three for example or four two and then hello for example and let's  just bring this right at the end run it you can see that we have hello right at the  end okay so basically this is how you create an array full of nulls and then basically act  upon it also if you want to create a raise so I can say array and have a look you can have  Boolean arrays byte arrays you can have double so empty array so basically I think it's the  same thing so empty oops or actually array in here and I think maybe this is the same as  the array of notes I think that's the same thing and double array float int and I  will look so you've got all of these constructs that allows you to create a  race now obviously also if you want to create an array of numbers for example you  can say int and then have a look array of so this will basically be an array  of integers instead of string and I think you have also double array of and all  the data types but basically this is pretty much what I wanted to cover about arrays and you can  do a lot more things in terms of initializing the array so for example if I wanted to so this array  of nulls if I want to fill the array in here right so let's say that I want to fill the array with  stars for example you can say array of nulls Dot and then you can use these methods so have a  look so you can fill you can say plus element required nulls you can reverse you can Shuffle  you can slice for reach which you'll learn later and then any as well so there's a bunch of these  methods that we can use including count as well filtering flat map so this is more advanced is  empty so in here you can basically say fill in here and we want to fill the array with stars  for example so if I run this instead of nulls it will have stars all the way and  then hello because of this line in here cool so we'll leave here for a race  and the erase is a very important data structure that you should know how to  use and what we need to cover later is how to iterate through arrays but this is  pretty much it next let's cover lists cool you've seen a race now let's work with lists  so the difference between arrays and lists is that lists are expandable whereas with arrays wants you  define the size you are no longer able to expand its size so if you want to create a list it goes  like this you can say Val and then I'm going to say list in here and then colon and we can Define  the type if we want so here we can say string so this is a list of string and here we can say list  equals to and then list and it basically works the same as arrays so you saw in here it was array  of so in here and here we have list and then off so you can say list of and then have the  size if you want to have an empty list you could say empty list in here and we'll cover  mutable list in a second so if I say list of in here and I'm going to add a new line and now I can  add my items so here let's just say again Jamila and comma we can say Jammers for  example comma we can say Saleh and in here let's say Jammers and in  here let's also say Peter for example cool and let me uppercase Jamila in here so now  let me actually also change this to names so we have names that contains in here four items now if  I was to let's just again say print line and names so right click run and this time we actually get  the list printed instead of the funny sequence of characters so you can see that we have Jamila Jama  Saleh and Peter so if you want to in here access for example the first element you can basically  say print line and then names Dot and here we can basically grab the index so I can say like this so  the same way that we've done with the race we can do it so 0 is the zero index we have Jamira if you  want to use the dot so there's a DOT get in here we can also use it but you can see the IntelliJ  says that we should use the index operator if you want to know the size in here let's just  duplicate this you can say names Dot and then size so if I run this you can see that we have four  elements so one two three and then four and from this point onwards it kind of works the  exact same thing as a raise because lists are built on top of arrays and if I want to know  whether Peter is there so I can say print line in here in the names dot contains and here  I can say Peter so if I run this you can see that this will give this true and if I basically  say it contains full in here run it we should get false and you've probably seen that contains has  contains all as well so basically you can pass a list of elements and check whether they all  exist in the list and um this is it now what about if you want to add a new element so this is  a difference between a list and arrays so lists are expandable whereas arrays are not and also if  you want to Omit this all together you can right so you could just do this so I'm just showing  the types actually cool so to add a new element so in here we need to say names Dot and here we  have an add method and basically this will not work and that's because this list right here so  this list is a read only list of given elements so if you want to add a new item you need to  use a different construct and that's what we're going to learn next but in the chill so obviously  there's more methods that you can explore in here so I can say print line and then names Dot and if  you want just go through all of these methods and basically just read the documentation on what  they do but for example we have first if I want to find out the first element run this and we  get Jamila she's the first also there's a lust so here you can see that we get Peter if you  want the index so in here names Dot index of let's just say Sally for example run it so Sally  is 0 1 and then two so we should get two there we go and this is pretty much how you work with  lists now bear in mind that this is a read-only list which means that you cannot add new elements  let me actually show you what you have to do next cool so if you want to be able to add new elements  to lists you need to use in here mutable list of so this in here gives us the flexibility so  here we can say string and obviously this is optional so let me just remove it so in here now  when we change this from list of to mutable list he just says by the name mutate so it means that  we can now add in here and remove as well so very important add and remove so in here let's just  leave all these operations as they were and so let's have a look in here so if I wanted to  for example remove Sally for example so you can say in here names Dot and then remove  and then in here we can remove first we can remove last we can remove if as well with a  filter but let's just say remove and then Sally now if I print lists so let me just duplicate  this and then print it right here at the end run it and now you can see that we have  Jamila James Saleh and Peter then in here I said names that remove Saleh and now Saleh  is gone cool so what about if I want to add a new element so I can just say names Dot  and then add so you can see that this time the add method works because this is a mutable  list so we have a couple of options we can add so in here you can see that we can pass the index or  we could just add it right at the end and you can see we can also add a collection so let's just say  add in here and let's just add for example Alex now if I print names so let's just  duplicate change the Line run this and you can see that now we have Alex and this  is the beauty of mutable lists right so basically it's also built on top of arrays but the beauty  is that you can add and delete elements from the array now you might be asking right so when should  I use mutable list versus a list or array so most of the times you're going to be using mutable  lists or read only lists and then the decision that you have to make is right so do I need to add  and remove elements if so just use mutable lists otherwise just use read-only lists and from this  point onwards all the methods are the same so here let me just say print Ln and I can say names  Dot and have a look last first we can replace as well we can remove we can set we can get by  an index remove if so this is to do with streams and you can check whether it's empty right so  is names for example is empty right the array itself so if I run this this will give  this false so it's not empty because it has four elements inside okay so if I was to  create so in here let's just say print line and then mutable and then list of and then let me  just take this and put it into a variable in here empty and then list and here we can  just say any so remember the any type which means that you can store any data  type you want so let's just run this and you can see that this is empty and if I  invoke Dot and then empty in here or is empty run it you can see that this  time it's true whereas before in here so this names right here is  now empty because it contains elements and to be honest this is pretty much it  next let me talk to you about data types and that is very important when it comes to  arrays and lists catch me on the next one cool let me teach you about the destructuring  Declaration when working with lists arrays and pretty much any collection so if we  want to grab Jamila Jamis and Sally for example under one variable we would  typically do this in many languages so here we can say Val and then I can say J  for Jamila for example equals 2 and the names and you've seen the index right now let's  basically get dramas so I'm going to say ja and here dramas is at position one and then Sally  I'm gonna say it's just s and Sally's at position two right now this here is cumbersome and never do  this in languages such as kotlin and JavaScript so what we can do is we can turn the following so we  can turn this into this so here let me just put a comment so what we can do is we can say Val  and then open parenthesis and I'm going to add a comment here basically comment all of this  so you have reference in here just like that and now I can grab the values in order  so here I can basically assign this to a variable so I'm going to say J for example  or let's just say one to two and then three equals two and then names so what this is doing  is basically destructuring the values for us so have a look so one now will be Jamila  two will be Jammers three will be sari cool so if I was to print for example  let's just say print Ln and then one and let's actually print everything in there  under one line so here dollar sign and then one dollar sign and then two and finally dollar  sign and three all right so if we run this have a look Jamila Jamis and Sally so if  you omit in here so I think we can even omit so basically if you don't want to pull  for example Sally but you want to pull Peter for example right which is the fourth  so I'm going to say four for example so four so now we are skipping right so we skip Sally and  if I run this you can see that we have Peter now let's actually check whether this is actually  variable so if I was to say underscore yes so basically underscore we can't really reference to  underscore because this is how we skip a value so this is kind of nice and the one that you should  really be aware so here this works with lists of array of so any collection really cool this  is pretty much it catch me on the next one whether you are working with mutable lists  arrays or regular lists never mix types so here never for example have a list that  contains strings and then numbers and then doubles in here so basically never do this  okay because if you start doing this it's going to be very difficult for you to build  applications and you're going to have to write a logical to accommodate different  data types so usually this is a big no no and hence sometimes you've seen in here so if I  say only strings so basically when you say in here less sign and then add the data type inside that  you want and then close so this has to do with generics you can see that I'm no longer able to  add numbers in here right so obviously if I remove this then the IDE knows that I'm only working  with strings then it tells me right so this is not needed and I'm safe so if you do this you  will encounter lots of issues potential bugs and you don't want to mix data types when working with  lists and I can guarantee you that you will never mix even if you feel like oh but I I think I might  have to mix data types trust me you will not mix so it's the same thing with for example a pencil  case right so pencil case you can only store pencils for example now obviously you could have  different types of pencils but they are pencils so you would install for example a spoon within your  pencil case or your socks or literally any other data type so socks spoon these are data types  within the pencil case so with programming is the same thing and as you write larger applications  you'll see that what I'm saying does make sense cool so I feel like I had to put emphasis  on this point so never mix data types when working with any data structure all right  this is my machete catch me on the next one foreign session you saw how to work with arrays and lists  now let's learn how to use Loops effectively to Loop through them and also show you some of  the cool things that we can do with loops so in here I do have two collections so the first  one is a list names and the other one is an array of integers so here let's say that we want to  Loop through them right so you saw that if you want to access for example so if I say print  a Ln if I want to get for example Mary in here I could just say names and then the index  if I want to get Ali names and then one if I want to get Alex names and then two so  this is the first index which is this one so basically this is the zero index one index and  then two index and if I say three we get a raise out of bounds here because there's no element  at index three in here and you can even see that um basically IntelliJ is telling me index  is always out of bounds because it knows cool but this is not a good approach when we want  to basically get all the values so for that we can use the loops so if we want to Loop through the  list of names we can use the for construct so four goes like this you say four and then you have a  temporary variable so here I can just call it name in and then the collection so in our case names so what this will do now so here we can  also add curly brackets and basically now we are within this block where we can do  pretty much anything that we want with each element so the first iteration name will be  Mary second iteration name will be Ali third iteration name will be Alex so if I was to say  print Ln and then name in here let's run this there we go so if I put this bigger you can see  that we have Mary Ali and Alex cool so this is the four construct so let's also print numbers so  let me just add a new line so let's just say four and then number and then in here  we can say in and then numbers so also if you are just executing one line of  code in here there's no need four curly brackets you could just say print Ln and then number now  one thing that I want to tell you is that so here so this is a variable name so this could be n  for example right so this I usually basically just say if I have something called numbers  or transactions I always have the singular so transaction number name instead of names right so  I always have this singular of the variable name cool so if I run this we should see that we have  one two three four five basically five numbers that we have in here right and the loop basically  knows when to start and when to stop and this is pretty much the way that you loop with kotlin now  in here let's say that within this for Loop we have each name in here so each name Mary Ali and  Alex and we want to capitalize the first letter of each name so M should be capital m capital  A and capital A for Alex so what we can do is in here so let's just basically say name Dot and  then we can say replace first and then character in here and basically this takes a character  so it's a Lambda expression and we'll learn more about Lambda Expressions later but  here I can say I T Dot and then uppercase so basically this right here will replace the  first character to uppercase and the result in here I'm just going to call it n for now I'm going  to say Val and equals to and then basically this now will be the replaced so we'll be marry with  capital like that so in here I can now say print and then n instead of the original name  that we get cool so let's just run this and if I scroll up have a look marry Ali and  Alex each of the first letters or the First characters are now in uppercase cool so this  is a quick introduction on how to use loops let me teach you about indices because sometimes  what you want really is to get the index instead of the actual value and then you can perform  other operations so in here let's change this from an array of instead of numbers and  let's just for example have characters so we could actually I think we have car array  of so here let's just change this from a B and then C and let me just  put this on a new line like that D and then e cool so now this is C I'm going  to rename this so C in and then let's just say letters in here and I'm going to say l or you  can say letter in and then letters and then print the letter itself right so if I run this  in here you can see that we have a b c d e now if I want to grab the index instead what we  can do is let's just put this inside of curly brackets so that we have more space so here I  can say dot and then indices so what this will give me now so I'm going to say index instead of  letter and if I print the index now if I run this have a look we get the index 0 1 2 3 and 4. so the  index is basically the position so zero index one index two three and then four now if you want to  grab the values themselves so let's just do this let's just print the index so we're going to add  this within double quotes and then here I'm going to have the index so here index followed by so in  here I'm going to say comma and I want to grab so I'm going to have dollar sign and then curly  brackets and here I'm going to say letters followed by the index so hopefully now you  see how this is playing together so as I'm looping I'm going to go to letters this  is my character array and the index will be passed inside here so the first time  is going to be 0 1 2 3 4. so if I run it there we go you see that we have 0 a 1 B and then  two c three D four e cool so the cool thing with this also is if you want to print in Reverse  right so if you want to print in Reverse what we can do is the following so we can take this  and let me just say print Ln and then reverse and I'm going to paste the exact same code  and now what I can do is I can say dot so right after I say letters dot indices  Dot and then reversed so this will now reverse and the index will start from the end  instead of the start so here if I run this so have a look so when we reverse now it starts  from 4 3 2 1 and then zero awesome so this is pretty much how you use the indices when it  comes to arrays now obviously this could be a list as well so here if I say list of right so  list of you can see that this will still work so it doesn't really matter whether it's a character  array or any other data type or basically whether it's a mutable list it will just work so that's  the beauty of kotlin cool so let me just stick with character array in here and this is pretty  much it for this video catch me on the next one with loops we have a concept of range and it goes  like this so if I have a for Loop and I want to print a particular range meaning that let's say  from numbers 1 to 10 for example we can say 4 I in and usually you see that here this is where we  pass the list or the array but with ranges we can say right so we can give it a range so this is  an integer so one between so dot dot and then the end so here let's just say one to five and  this is IntelliJ telling us the actual range now if I print this let me just print it like this  so print and then I in here so if I run this you can see that we have numbers one  all the way to five so if you want maybe um 10 to 100 for example you can do it so if I  just run it we should see all the numbers from 10 all the way to 100. cool so let me just  stick with small numbers and this is nice what we can also do is we can print in Reverse  so if I say four and then I in and in here five and then dot dot and then one in here so what  I want to do first is I want to show you that if I try to do this and run this and here we  get nothing and that's because if you want to print in reverse all we do is you don't say  dot dot but instead you say down and then two so five down two and then whatever the stop  number that you want so if I run this time you can see that we do get five  four three two and then one awesome so this is pretty much ranges and  one other cool thing that we can do is so let me just duplicate this right here so if you  want to step so we can actually use the step and basically we can step right so the default  is one but we can step in twos so one to five but we're going to step every second element so  if I just so in here let's just have print line and then I'm going to say steps so that  we basically have a nice output so also print line and then here down two and here I'm  just going to say print line and then range all right cool so let me just comment this one for now  so we can have a better output so if I run this have a look so we have steps but have a look we  have one and then we step from one to three so this is we're stepping in twos so we have one  and then we're stepping in twos one three and then five so you can see this is beautiful also if  you want to you can basically step in here so step and then we can say step and then two  as well and coming down right so five three and then one so if I run this you can see five three and then  one and this is pretty much it so let me just say steps or step and then down  in here cool so this is how you use for loops and range as well as the down to as well  as step two have control on how you iterate if you have any questions drop me a  message otherwise catch me on the next one you saw that you can loop with lists and  arrays but also if you have a string in here you can Loop through a string as well so  it's the exact same thing and let me show you something you can say brand Dot and then if you  say f o or and then if you say four IntelliJ Auto completes this 4S right so here I'm going to  say the letter in brand and I'm going to print l and then obviously you could perform anything  you want right so you can have if statements and whatnot but if I right click and then run you  can see that we have Amigos code in here and then here as well obviously if you want to  use the indices so dot and then indices Dot and then reverse basically you could use  everything that we've learned so far but I just thought that I'll let you know that you  can also Loop through a sequence of characters foreign another way that we can Loop is using the  for each construct and this is found in many languages including Java JavaScript and kotlin  also has it of course so if you want to Loop you've seen that you can say four or you can use  IntelliJ order completion so names and then four here and then we get the construct and then we  can print right so here let's just say print line and then name okay but we can also use  the for each which is a better syntax in my opinion and the one that you will use quite a  lot and if you don't need access to the indices then this is a good approach so you basically  say so let me just put it right above you say names dot so your collection and then for each  so for each takes a consumer in here and then inside we can add curly brackets and here we  have access to it so it is a placeholder that corresponds to the value for each element  so now I can just say print Ln and then I T just like that so you can see that also IntelliJ  says that move Lambda argument out of parenthesis and we don't actually need you know parentheses so  we could just do it like this which is much better have a look so names for each and then curly  brackets and then you basically say print Ln and obviously if you want to have multi lines just  like that and you can see IntelliJ is actually even telling you the data time for it so this  is quite cool so this is the exact same thing as this in here so let me just comment this out so it  doesn't execute let's right click run and have a look we have Jamila Jama Sally Peter so literally  just use any array and just use the for reach and you can see that it's quite neat cool there's  more to it when it comes to functional programming which will cover later but for now this is pretty  much everything about the for reach construct cool another construct that allows us to Loop  is the wall and do while Loops so let me show you and even then Java then this is pretty much  the exact same thing and let's say that we have a variable in here I'm going to call it I and  we're going to oh actually let's just call it number equals to 1 in here and let's say that we  want to Loop through while the number is less or equal than 5 and then print and also increment  the number so the way we do it is using the while construct and here this is an expression right so  I'm going to say while number is less or equal to 5 in here so if this is the case right I want  to print the number so I'm going to say print line and then I'm going to say number and then  here dollar sign and then the number itself and obviously here I need to increment number  so I'm going to say plus plus and then number cool so if I run this right click run you can  see that we have number one two three four five so basically this is from one to five but if  you want the reverse right so from five so five all the way down to zero you say five and then  basically you reverse so while number is greater or equal to zero and here we're going to decrement  so minus minus and the number run this and you can see that we have five four three two one and then  zero cool so this is the while loop and obviously if you have a given array you can actually Loop  through the array as well so if we have a real list basically so if we have for example in here  let's just have a string let's just have a string so here I'm going to say brand and then equals to  and then Amigos code so this will be Val and here I'm going to have the index so VAR and then index  equals to and then brand Dot and then length minus one right because the length is one two three four  five six seven eight nine ten right but the index is from zero right so zero to nine so this is me  looping from top to bottom right if you want the reverse you just say zero so Zero from here and  then moving forward but I'll show you in a second so here if I now say that the index so the index  so while index is greater or equal to zero in here I'm going to say index minus minus so decrement  the index and then here I'm going to print brand and then index so brand and  then index and index can type today and obviously I need to have curly brackets  because it's not just a variable but it's a more complex operation in here right cool  so if I run this you can see that basically e d o basically Amigos code in Reverse if you  want from beginning to end you just change this from this to zero and let's actually take this  instead and just reverse so just like that and then obviously we have to change the sign so this  is now less or equal and then here we increment the index plus plus and then index run this and  now oops it shouldn't be number but it should be um let's just print like that right so  it should be that so if I just run it there we go so you can see Amigos code so  this is pretty much how you use the while loop and obviously I said this could also be  for example so we can change this from array of and here I'm just going to say uh and then m  I so basically Amigos but I'm going to leave it here and here instead of length this is  size and in here so this is brand instead and we can remove the necessary string  template and if I bring this we should have Amy should be Amigos code but you get the gist  cool so this is how you use the while loop and over C remember the difference between vowel  and VAR so the reason why I'm saying VAR in here is because here I'm reassigning the value of  index so if I say Val in here this will not work cool this is pretty much  it catch me on the next one okey dokey you've seen the  while loop which basically works like this and here if I say for example true so this is the Boolean expression that it takes  right so while this is true if I print in here so if I say hello so this will actually print  forever okay let me just try so you can see so you can see that this is actually printing  forever and let me kill the process by pressing the stop button and there we go so basically  if I change this to false in here and run this this will never print nothing now if you  want something to be done at least once and then continued operation while your condition  is true what you can do is you can say do and then wow so now all of this  goes so the body in here has to go and it goes like this right so do something  so here we want to print while a condition so in our case before you saw that while  false and then inside of the body nothing gets printed but now if I run this so I've just  indented things so do this first while false so no matter what this will always be printed  or executed at least once so if I run this you can see that we have hello once and if I  change this to true in here this will run forever so let me just stop this and you can see  that it's running and basically if you want to perform something at least once and then  have your condition then use the while loop cool this is image it catch me on the next one together cool now let's learn about the break and  continue keywords so let's say that we want to skip the number two while looping so  here let's just say four and then n in nums and let's say while we are looping if the  number equals to 2 we want to continue I.E we want to skip so here let's just say print  and we're going to print n for now and if I run this you should see that we have one two  three four five nice and easy so if I want to skip number two and not print it I can say if and  n equals to then inside here I can say continue now what this does it basically if this  condition is meant continue was simply skip whatever comes so whatever line comes after  line six and then go back to the next iteration so if I run this we should skip number two so  you can see that one and we went to three instead let's say that you want to change this  so that if the number is even you want to skip it so you can say if n and then  modulus and then two equals equals zero so if there's no remainder then we know  that the number is even so if we run it you can see that now we are only printing odd  numbers so one three five so if you want the reverse you could just say not equal and then run  it and you can see that now we are only printing even numbers so this is the continue keyword  now let's say that so in here we also have in you know six seven eight and even more numbers  and as soon as the number so as soon as the number is bigger than 5 we want to come out  of the loop all together so for that we can use the break keyword so here let's just say if  and then n greater than five we want to break so break and obviously we can basically have curly  brackets in here and then just say break or you could just leave it like this so it really depends  on the formatting style that you and your team decide so now if the number is greater than six we  don't even want to go back to the next iteration but we want to come out of this Loop all together  in here right so let me just say print and then some other code so if I run this  you can see that we only print two four and then six and we continue to  some other code now obviously here I said six and I meant five my bad so this is five not  six but five so we should print even numbers up to five right so two and four and then as  soon as the number is bigger than five we skip all of this by coming out of the  loop so let's just run it once more and there we go and this is pretty much how  you use the break and continue now one thing to bear in mind is so I want to quickly show  you that if I have in here so nems dot forage and if you think that you can use the break  and continue inside you are wrong so if I say I T So if I T equals to 2 for example in  here I want to continue so if I say continue so this is not possible have a look so break and  continue are only allowed inside a loop so this is also Loop but it is slightly different and  we'll explore the functional programming style later but also if I want to break out of this  Loop in here gonna break out of this Loop I'm not allowed and it's the same thing with Java  cool so let me just say this is not allowed and then we have a multi-line common in here so  just like that and then end it right here okie dokie this is pretty much everything for break and  continue do so for now catch me on the next one foreign let's focus on functions and functions basically  it's what makes a program in general so if you have an application and you want to perform  a bunch of business logic I.E all this all the decision making all the steps required in  order for you to build a large piece of your application functions is the heart of pretty much  everything now in kotlin this is a function in here so you've seen that when we have basically  print line hello in here so fun and then main so this is the construct for creating a function this  is the name so this is a special name because this is the entry point for our application and then  here this is how we are invoking the function and then within it we have the parenthesis and Then  followed by curly brackets and inside this is the function body now here you see that the function  name is called Main and inside I have a sequence of instructions so in my case print Ln print Ln  as well so if I put my mouse in here println is another function have a look it's a function so  public inline fun the name is println and then it receives a message of type any and the return  type is unit which we'll cover in a second as well so you've seen also that in here so I can say  hello but if I say hello Dot and then uppercase this is also another function right so these are  predefined functions or built-in functions that we can use so have a look so this is public inline  fun string and then uppercase it returns a string and basically it returns a copy of this string  converted to uppercase using Unicode right so in programming we basically use so also  you've seen that we can get for example indices right so here if I say in this is so in  this is actually this is a variable in here but have a look I think we used to be placed before  so replace first car right or replace in here and then lowercase so all of these are functions  so if I run this in here so let me just run this and you can see that we have hello been printed right so this is a function called print  Ln and inside we have something called an argument so these are the arguments so what  goes into a function and I'll show you basically arguments and parameters in a second so in this  section let's learn how to work with functions okay let's create our very first function so in  here literally outside the main function let's have our function that pretty much  will grit so let's just say fun so this is the construct for creating a function and  here I'm going to say great so we're going to say grid and this right here is the name of  the function and then just add parenthesis and in here have curly brackets and this is our  function now inside of this function called grid we can perform anything we want right so this  is where we put all the business Logic for our application or for what we are trying to do so  in our case I'm simply going to say print Ln and then I'm going to say hello so basically  let me just get rid of this print Ln in here this is our function now if I want to  invoke this function called Grid in here inside of this other function called main so this  is where our application runs I can just say Grit so I just named the function in here so just name  the function right and if I want to execute the function I just add parenthesis so this is  actually invoking the function if I run this we should see that we have hello  right so if I change this to hello and then maybe add an emoji and  then say hey for example there we go and run this you can see that we have  hello in here if I comment this out in here run this doesn't get executed so even though we  have oh actually sorry I didn't want to do this I wanted to comment out this one in here so even  though we have a function in here it's not been used anywhere and even IntelliJ it's actually  graying out the function name so as soon as I run this first we get nothing but if I uncomment  this now the function becomes blue and we know that it's being used so this in here is a  function now if I put a mouse in here on top of this function you can see that this says public  and then fun and then great colon and then unit so basically I can do this I can say public and these  are part of the access modifiers and we learn these later but let me just remove this because  it's redundant so by default these functions they are public unless you want to say private in here  which means that the only thing that can access this function is anything within this file in here  so let's just get rid of this and not complicate things at this point and access modifiers not  just work with functions but also with variables cool so in here if I put a mouse in here have a  look public fun and then great colon colon and then unit so in here if I say colon and then a  unit so this is a default return type which is unit if you come from java this is the same  thing as saying in here public and then void and then greet so greet in here so great is  the name of the function void it means that this function doesn't return any value so let  me just get rid of this and if I press command and then you can see that I can navigate into  the unit definition so let's just go into it or you can press command and B and also you can  see the keyboard shortcut Down Below in here so in here public object unit the type with only  one value the unit object this type corresponds to the void type in Java all right so basically  this is actually redundant so if your function doesn't return any value then basically you can  omit this all together okay so you don't need this and it's the same with the main function  as well so I could actually say in here unit it's the same thing but this is redundant all  right so this is your first function with kotlin so fun is the keyword for creating functions then  the name then here you add parenthesis and inside parenthesis you can have parameters So currently  there's nothing right so I'll show you parameters also in a second and this is pretty much it  let's carry on with functions in the next video all right now let's say that our function  we want to have the ability of passing an argument into the function so when we invoke  the function grid we want to pass for example the name and then we should be able to print  hello and then basically the Emoji and then the Emoji followed by the name of the person so  how do we do that well with functions we have something called parameters so in here we can have  a parameter and let's just say name for example now when we say name we can't just say name  because we need to specify the actual type so what is the type for the value which will  be passed so here let's just say string and now you can see that this grid  function here is complaining because we need to pass the name so here let's just  say Jamila for example so this is the name and here we not using it so if we run this so we  still get hello in here but really what I want is hello and then Jamila so let's just use it so here  we can basically add dollar sign and then name cool so let's just run this and you can see  that we have hello Jamila now the beauty of this is that I could invoke the exact same  function in here and I can say Alex for example and here let's just say Bob as well if I run  this you can see that we have hello Jamila Hello Alex hello Bob right so this is the video of  functions now this right here is the parameter so a function can have so function can have zero  or more parameters and then the values that go inside so the values that go inside these  are the arguments also just bear in mind that IntelliJ is actually adding the hint for the name  of the parameter so here Name colon so don't type this basically right so this is IntelliJ and I  can get rid of it by pressing option and then I can say do not show hints for current method  and you can see that it basically gets rid of it so let me just undo in here and sometimes  I kind of like this and it's really up to you but basically these are parameters and these are  the arguments the different values that we pass so also if you want to pass for example H so  let's just say comma and then we can say h and here the H is an integer right now we can  basically say if and then h in here is greater or equal to let's say 16 we're going to  say print and then name is an adult else we're going to say basically the same thing but I'm going to say is not  an adult and now here we have to pass the H so let's just in here say comma and we can  say 22 for example in here we can say also 16 and let's say that Bob is 11. cool so you can see that now we have two  arguments and two parameters if I run this there we go so hello Jamila Jamila is an adult  Hello Alex Alex is an adult hello Bob Bob is not an adult cool so you can see that basically this  function now we print we have some logic in here and if it's an adult or not we basically perform  some if else statement and generally this is how we write our business logic but in this video  you've learned about parameters and arguments foreign other thing that I want to cover when it comes  to the arguments is that in here let's say that you want to switch for example first you want to  pass the age and then the name for example you can do it so here what we do is we basically  get rid of this for now and now I can say h equals 2 and then 23. comma and then I  can say name equals to and then Jamila so this is kind of the same thing as IntelliJ is  doing but basically here now I'm being explicit on the actual ordering that I'm passing these so  sometimes you might have you know a long list of arguments and you want to be able to Define so  you want to say h equals to 23 name equals to Jamila so and so forth you can also do it so  here if I run this nothing will change so his exact same thing hello Jamila Jamila is an adult  right and you could also do the same for these ones this is what's known as named arguments cool  next let me talk to you about default arguments all right now let's learn about default  values for arguments so sometimes you might not necessarily want to pass a value into  a function or basically an argument what kotlin allows us to do very similar to golang and also  JavaScript is that we can have a default value so let's say that for example we don't want to pass  age in here so what we can do is we can say age and then colon int equals to and then the  default value so here let's just say minus one so we're going to say -1 and now  we can have a bit of logic in here so we can say right so if the age in here is  greater or equal to 16 we print is an adult and also let's just have another if statement in  here so let's just say if and then H equals to -1 so we know that H is not provided so obviously  there's better ways of doing this but this just allows me to illustrate the purpose of default  arguments so here I'm going to say print Ln H not provided for example and what I'm going to  do is we could actually you know exit out of this Method All Together by using the return keyword  but let's learn that later but now it means that for example within Alex in here I can remove the H  altogether have a look so this is good so now Alex age will be -1 because it's not provided so if we  run this let me just add a print line but between between each Grid in here so print line  as well or actually better what we can do is so let's just remove this print line  as well and we can do it right at the end of the method so let's just say print line so  this is much better cool so if I run this now what we should be able to see is have a look hello  Jamila and then Jamila is an adult Hello Alex and an age not provided Alex is not an adult so I'll  show you something else that we can do so that we don't print this line in here and then followed by  Bob Bob is an adult so both Ali so both Jamila and so both Jamila and Bob they have age and with  Alex because we didn't pass H the default value is -1 and obviously if you want here as well so  for the name you could have equals two and then the default um and then the default value  but in our case we want name to be mandatory cool this is pretty much everything about  default arguments catch me on the next one foreign what's really cool about kotlin is that you can  patch functions as arguments so functions within functions so in here let's say that we want to  have another function let's just say function or fun and I'm going to call it and I'm going to call  this as Foo in here and within this full function I want to be able to pass another function as  argument so the way we do it is we can say bar for example this is going to have the type as this  in here so this is literally a Lambda function in here so it goes like bar and then basically this  is a Lambda function and in here we need the body just like that and now we can have some logic in  here so let's just have a simple print I'm going to say bar function in here and right after it  I can invoke this function which is bar so I'm going to say bar in here and invoke it like so  which means that now if I want to use this full function I can in here let's just add a comment  so that we basically organize things properly and now within our main function if I was to use  the foo so Foo in here I'm going to say Foo and I've got a couple of options so here I can  basically invoke it like so and then say bar equals to and then curly brackets and this now  is the function so here I can basically have now any logic I want so here I can say for example  another print and then bar as a function cool so let's run this and you should see that what we  get is bar function and then bar as a function I can basically now take this Foo invoke it  again and this time I can basically say for example baz and then baz so this right here is  anything that I want right so let's just run this and you can see that now this is bar function  and then bars Buzz so you can see that this function has a different implementation than  this one when the function is passed onto it now you've seen defaults so if you don't want to  pass a function what you do is basically say equal and and you can have an empty implementation  like so right so now here I don't need to pass the function in here so this is kind of cool and  the other thing is so in here we can basically so let me just duplicate this in here so we can  pass the function in two ways we can have it as named argument in here or so we can take  this in here let's just get rid of this like so and we can pass it like this have a look  so in fact we don't need the parentheses and this is basically invoking the full function  and then passing the other function inside so it's the exact same thing as we're doing  here so if I was to run this in here and um let's just say 2 for example run it and you can  see that it works the exact same way so in here bar function bar as function and then bar function  bar as function two and then bar function and then here this in here we didn't pass any function and  it just gets a default and we don't do anything so this is a really nice feature when you can  pass functions within functions and bear in mind that this right here so in here so this right here  will only work when the function so the function in here so the function is the last argument  yeah so if it's not then you have issues so here if I was to say for example let's just say  name and this is a string for example right and let's have a default value of empty for example so  now you can see that you are no longer able to do this right so you can only do this when the last  so the last argument of it is the Lambda itself so here let's just switch places and now you can  see that this in here does work so if this is a bit complicated don't you worry because as you  start to write kotlin code and do more complex stuff then all of this becomes second nature and  one last thing that I want to mention is so here we basically have a unit so in here have a look  so name and then bar so let's just basically put this on a new line like so so this is a unit but  this could return any data time so if you want the string you just say string if you want an integer  then you just say integer right and obviously here then you have to return the default value as well  that comes with it but in here you can see that this now fails because we have to return a number  for example there we go cool so let me just put it back because it's easy to understand the way  I've done it but at this point if this is a bit confusing don't you worry about it seriously cool  this is pretty much it catch me on the next one let's go back to this function called grit still  under the functions.kotlin file and in here remember we saw that if the age is -1 basically it  goes and prints all of this but let's say that I don't want to continue at this point and meaning  that I want to bail out so what we can do is within the condition so here if and then age  right so what we can do is just say return now when I say return it basically everything that  comes after this line in here so outline 27 will not be executed so you saw that in  here when we have I think it was Alex right so before it was printing that Alex  was not an adult in here right because he goes in here so Alex H is minus one which is a  default but all I want is basically to come out of this method and not even bother to was coming  next so this is when you use the return keyword let's just run this and now if I scroll up you  should see that we have hello Jamila Jamila is not an adult and then Hello Alex age not provided  and then we don't have basically Alex is not an adult because we exited the method all together  right so here we did exit method all together and let's also include a new line so we can include  the new line by saying backslash and then n and if I run this again so this time we  should have a new line in between so here I want to have a new line in between here Alex  Asia provided a new line and then hello Bob Bob is not an adult awesome this is pretty much  it also what I think maybe you can include the age in here as well if you want so  name and then in here let's just say h and then Dash and let's just  take this and put it right here and I think now we have better messaging so if we  run this you can see that now we have Jamila 23 is an adult Alex agent or provided Bob 11  is not an adult cool this is pretty much the return keyword right so if I was two in here  let's just write in here let's just return so if we return at this point nothing will be executed  you can see that IntelliJ is telling me hey what's this so if I run this you can see that nothing get  executed apart from our functions within functions so this is pretty much it so what I'm going to  do actually is let's just take this right here and I want to say functions as arguments there  we go cool and you haven't learned about private so let's just remove that and here if you  want to uncomment this and run it just do it all right so if I run this the output should now  be less verbose have a look for nothing but all I want is within the grid I want to get rid of  this because this is pointless all right this is pretty much how you exit out of a method  whenever you want using the return keyword all right so so far you've seen that our  functions they really don't return any value right so you saw the in here the unit so  the unit type and basically our functions they don't return anything so let's learn how to pretty  much return a value from a function so here let's say that we want to have the ability of doubling  a number so if we pass 2 the output should be 4. so here let's just say fun and then double so  this will be the name of the function and here we're going to accept a number so I'm going to  say n for number and the type will be an integer and inside here you've seen that basically all I  do is this so print Ln and then I can do n times and then 2 right so if I want to use this and let  me just comment this once more so if I want to use this I can just say double and here and then I can  say 10. so this will be 20 right so if I run this there we go we have 20. now I basically want  to return the value instead of printing okay so this right here doesn't return anything so  it's the same as the void in Java but all I want is to return a value so if you want to return  a value from functions you basically say return so this is the returned keyword and  you've seen that it can be used to exit also out of the function and also  what we need here is to say right so outside so outside the last parenthesis  so the closing parenthesis just add colon and then the return type so here I can say  int so this function returns an integer and have a look so now this works beautifully so  this now if I run it will not print right because this Returns the doubled number which is 20. so  here let's just store this into a variable vowel and then I'm going to say d for double equals  to and if you want actually you could just print just like that if I run it we should  get 20. so this is really cool and yeah that's pretty much it obviously if you  want to return all sort of strings you can say string in here and this will not fail because  the data type is different but you get the chest awesome this is how you  return values from functions okay if your functions return a single expression the  curly brackets can be omitted and the body is specified after the equal symbol so meaning that  in here so I can simplify this entire function because here I'm just returning so I'm getting  a value and then I'm returning so if this is the case then I can just replace this function let  me just comment this out and we can rewrite it as follows I can say fun double so everything is  the same so n and this will be integer and then I have to specify a dividend type which is int and  here this is what's different so now instead of saying curly brackets I just say equals and then I  can just basically have my expression so here I'm going to say n times and then 2. so have a look  how beautiful this is right so function as single Expressions right so this is something that Java  really doesn't have and I love this so you can see that nothing changes if I run this there we go  have a look 20. we have the exact same output cool so this only works when your function basically  does one and only one thing so for example if you were to have this function here so let me just  put it back and let me call it double and then two for example so if you were to have print line in  here and need to a bunch of other stuff before you can't really go from this to a single expression  function right so only if there's one value so basically one return statement for example cool  this is pretty much it catch me on the next one so you saw functions the return types and body  and whatnot let me quickly touch on the return types which is very important so if a function  in here has the unit remember the unit this is optional right so if for example this was  unit in here and if I remove this in here this actually is optional okay so  void right so if it's not unit then so in here so we have an integer this is  always required so the return data type when it's a single function expression in here we  can actually omit this so we can get rid of this so we can do just like this and this works  but only for single function expressions so I'm going to leave this in here as is but  bear in mind that if it's a single function expression you don't need a data type and  if it's void right so if it's void so the unit you don't need the type as well but as  soon as you have the curly brackets you will always require the return type for your functions  this is pretty much it catch me on the next one foreign working with functions if you want to return  multiple values from your functions it's possible by using the pair data type as well  as the triple so for example with golang you are able to return multiple values without even  having to use the pair or triple but in kotlin if you want to do that we have to use the pair  data type so it goes as follows so here let's just have a function so here I'm going to say fun  and then I'm going to name it as 2 and then values and what we're going to do is we're going to say  colon and the return time for this will be a pair just like that and here we have to have  the diamond and now what is the data time so let's just say we want to return a string  and also an integer just like that all right now within here we can pretty much return so if  you don't have any logic to do so let's just say return and here I'm going to return the string so  here I'm going to say Amigos and we have to say 2 and then the integer type so here let's just  say 20 for example so this is how you return multiple values from within your function if you  want to return three values you basically do the same but here let me just have this as three  values and here we're going to name this as triple so here just say triple and basically  the data type let's also have an integer or let's have a character so Char in here and the  triple is a little bit different in a sense that we say triple in here and we pass the values so  first let me put this on your line then we have the second then we have the third so here I'm  going to say the character is Zed for example just like that and we need to comma here and  if I indent this cool put this on your line and you can see how this function is looking  like so fun tree values the return type is a triple it returns a string an integer and a  character and when we say return it basically Returns the triple in here so we can change these  to single function Expressions so this can go and here and just say equal and same as return and  here right so this is beautiful code actually so have a look oops not like that but like this  so if you wanted to right so get rid of that and get rid of that and this and say equals  and voila cool so let me just put this one back so you have it for reference there we go and  this is pretty much it now one cool thing about returning multiple values is that you can  destructure them so whenever you want to use them you can destructure them as follows so if I  in here within my main method if I want to consume them for example let's consume the two values so  I'm going to say two values right so two values and the values will be stored into  a variable so let's just say Val and now I can say V1 for Value 1 and then V2  equals 2 and the two values and the same with triples right so here I'm  going to say three values and here I'm going to name this as  let's just say T1 t two and then T3 and if you want to print them let's just print  them so print and here I'm going to print the one and then also V2 let's duplicate this  and also change this to T1 T2 and also t and then three with dollar sign and  let's basically have a print line in here so if I run this you can see that we have  Amigos 20 Amigos 20 and then Zed right so basically the values here they are the exact  same thing so I could have changed this to code for example and then 90 or  0 it doesn't really matter run it and there we go so this is actually beautiful  stuff so these are the values so two values and then three values one two and then three  and actually one thing that I forgot is with pairs in here so you can say Amigos and then two  or if you also want you could use so let's just duplicate this and I'm going to say two values  and then two and you can just basically say pair like that and instead of using D2 so I prefer  two so it's nicer but you can also do this okay so either this or this awesome this  is pretty much it catch me on the next one foreign let's learn about classes and objects which  is pretty much the heart of programming in many programming languages where we kind of have  classes and these are the blueprints and then we have the objects so these are the actual  things that we create from the blueprint so classes is actually found in many  programming languages and kotlin also has the exact same construct so if you want  to create a class you use the class keyword in here and then you give it a name so here  let's create a class called smart device and add curly brackets and this right here is  the smart device class now this class right here it's the blueprint so blue and then print  and basically it defines how smart devices are created so you define the properties so here  Pro protease and also behaviors so here we are talking mainly about functions right so these  are the functions and these are the variables so either with vowel or VAR so we'll come back to  this in a second but basically you have a class in here where we can define properties and behaviors  in here so let's focus on these later but this is pretty much the construct of how to create a class  now the way that we're going to use this is within our main function in here we can say it right so  now I want to say Val and let's say that we have a smart device and we're going to name it as  TV equals to and then just say smart device now in languages such as Java you have to say new in  here so this is not needed in kotlin and all you do is you just refer to the class name just like  that if we want for example a phone in here we say phone equals to and then smart device now you  can see that this right here is the blueprint so the class is the blueprint and then the TV and the  phone these are the objects so we have two objects now classes is something which is not new to be  honest so if you look into array for example so array in here so array Mouse in here have a look  so if I open this and just go into the array dot kotlin file and scroll to the top have a look  public class and then array so this in here has to do with generics which means that you can  pass either a string or an integer or a double but basically this is a class right and you  learn about Constructors as well in a second but with kotlin we have many of these  classes and in fact if I open up project and in here I think we can locate so if you click  on the array.kotlin and then click on this button select open file so this should take you to where  this class is located and you can see right here so if I Collapse this have a look so all of these  are classes you've seen Boolean you've seen car or character you've seen double enum float int  so int is also a class if I click on it have a look public class int have a look number short  throwable so including string right here and all of these are classes and if I Collapse this you  should see that there's a bunch of other classes right so have a look pair for example you've  seen the pair class in here right so it has um the first value and the second value and in  here you can find a list of a bunch of classes so what we want to do really in a nutshell is for  us to have our own classes so that we can model and represent the real world and with classes  we can pretty much build anything awesome so now that you basically know that a class is a  blueprint and when you instantiate in here this right here is the object so TV and phone are  objects and that the blueprint that was used to create these was the Smart TV device awesome  this is pretty much it catch me on the next one awesome in here let's say that within our  blueprint so this class called smart device we want to have some properties so maybe you want  to have the brand you want to have the color you want to have the price so basically these are  the characteristics for a smart device also the type whether it's a phone whether it's a TV right  so in here we have all these properties and then the objects themselves they're able to decide  which characteristics that they want to take from the blueprint so in our case let's in here  say that we have this class called smart device and we want to have the property in here we're  going to say VAR and let's say brand for example so here we need to specify the data type I'm  going to say string and here I'm going to basically have empty string okay so brand with  an n in here cool so let me actually get rid of this in here and this as well and as we progress  you'll see how this will work out awesome now we have this property in here called brand the type  is a string you can pick literally any type you want let's also have another one so VAR and then  price for example and this will be let's just say double for now in here and equals and we're going  to say 0.0 so this is the initial price cool now you see that we have two smart devices one it's  a TV and the other one it's a phone so maybe we want to also represent the type now for the type  I'm going to show you later something called the enum which is a better way of representing types  instead of using strings so let's just keep these two properties for now so let's now in here when  we have TV let's just say TV we can say TV DOT and then have a look I can say brand equals  to and here I can say for example Samsung and I can also say TV DOT and then price and let's  say that this TV in here is I don't know maybe one thousand just like that right so 1000 if you want  currency and whatnot you can also have it cool so this is the TV and you can have brand then model  and you can basically model this the way you want but let's just have brand and price let's do the  same for the phone so here I want to say phone Dot brand equals to and in here let's just say apple  and now I'm going to define the price so phone Dot and then price equals to in here we let's just  say iPhones are quite expensive so there we go so let's just say 1200 just like that all right and  if you want you can basically say apple and then iPhone I don't know what's the latest model  13 14 like I don't even know but it doesn't matter right so apple and then iPhone let's just  see the iPhone and then here you can say Samsung Smart TV and then Q is it qled something like that  cool so you can see that now we have two objects in here and they are completely different from  each other now in the real world this is actually a thing right so this could be your TV and this  can be your phone we can see that we use the same blueprint called smart device because both of  them are smart devices to create two separate objects and you can see that in here this is how  we define the properties now one thing to bear in mind is remember the difference between the  vowel and VAR so if I was to change this from VAR to Val check what's going to happen so have a  look the brand for both objects in here I cannot do this in here right and that's because the  reassignment right so we cannot reassign the actual value so we'll come back to the vowel and  also data classes later so this has to do with immutability but for now let's just use the VAR  that basically allows us to assign the values in here after we create the object like so cool next  let's go ahead and talk about Gettys and settings all right so we have the TV as well as phone  if I was to print let's just say print Ln in here and let's just have quotes in here and let's  pretty much just print the TV so I'm going to say TV DOT and then brand followed by TV DOT  and then price okay so let's take this and then put it here and this will be phone so  phone dot brand as well as price if I run this you should see that we have Samsung Smart TV qled  and then the price and an Apple iPhone and this is the price cool now we are able to get the brand in  here because of this so here I'm going to say get in here equals to and then field and the same for  the price so let's just add in here get equals to and then field now this is actually built into the  language and literally you actually don't need it but this is what's happening under the hood and  you can see that IntelliJ is even telling me that this is redundant so redundant get because by  default this is included hence when you say in here tv.brand you are allowed to do this right  so if I was to change this to Foo for example Foo in here so if I run this you can see that  now in here Foo is replaced with the actual name right so uh oh actually brand my bad right  so Foo is replaced with the actual brand for both in here this brand and this brand So  when you say in here so if I go back get equals to the field is just  going to return this field in here cool so this is how Getters work in kotlin also  we have Setter so here just say set and then value and then inside I'm going to say field so the  field so this field called brand is equal to the actual value so when we say in here price right  or either brand equals to the value so the field equals to the value in here so Apple iPhone so if  I was to change the value in here to bar this time so you should see that if I run this bar is  replaced in both instances so this is how basically Setters work now obviously here if you  want to perform something so maybe you want to have I don't know you want to basically uppercase  everything so uppercase in here or you want to replace the first case with an uppercase you never  know right so this is how you do it and maybe you want to perform some validation before you set the  value so here you can also perform whatever logic that you want to be honest so if I was to run this  you should see that now Samsung TV is Mark you led all in uppercase so this is basically Setters now  in here so let's just leave it as value so value and we can take this and basically put it the  same in here for the price but as I said this right here it's redundant we can get rid of it  and in here as well and also here awesome so I just feel like this is very important for you  to know what is happening under the hood because Getters and Setters is something that you find in  Java for example and in kotlin they work a little bit different cool if you have any questions drop  me a message otherwise catch me on the next one all right so you've seen properties in here  so these are the variables that specify the attributes of the class object now let's  look into the methods so methods slash and then functions and the functions are simply the  behaviors of what the object you create have the capability to perform so in our case in here so  a smart device might be able to switch on switch off might be able to increase the brightness  decrease the brightness might also be able to increase the volume record shows and have a  list of apps and all of that stuff right so basically those are the functionalities right  so installing an application and installing so all of that is the functionality right so if  you for example take this same example to a class called person right so the attributes  would be name skin color languages and the behaviors would be eat sleep play games and  whatnot right so in our case in here so for our smart device let's just have two methods  and in here we're going to basically say fun and basically the behaviors are pretty much  functions and here I'm going to say turn and then on and in here we're going to for now let's just  print line and then here I could use the brand is switching on and let's have another method in  here I'm going to say turn off in here turn off is let's just say switching and then off all right  cool so you can change the name here switching on or turn on it doesn't really matter so now this  right here is what the blueprint allows objects to perform so in here let's just scroll up let's  use our phone for example if I want to switch off the phone I can just say phone Dot and then  turn and then off for example so if I run this you can see that have a look Apple iPhone is  switching off so if I was to do the same 4 let's just say TV in here so TV right so our TV you should see that we have in here Samsung Smart  TV uq LED so it's a long name is switching off and Apple iPhone is switching off so you can see that  there are two completely independent objects and when we say brand in here it refers to the current  instance of the current class right so this is pretty much how you define behaviors now what we  could actually do is we could mutate this Behavior so we could have a variable in here so I'm going  to say VAR and in here I'm going to say state and the state in here will be a Boolean and  initially it will be off right so let's just say false or we could say is and then on for example  right so is on or is Switched so let's just say switched on so this is false now when I turn on  in here I'm going to basically say is switched on equals to and then false or actually sorry this  is true my bad and let's take this as well is switched on and here so when we invoke turn off  this will be false there we go cool and then in here let's just basically have another function  in here another Behavior so I'm going to say fun and in here I'm going to say get device state so  what we're going to do is we're going to say print Ln and here I'm going to say dollar sign and then  the brand plus d is switched on I'm going to say is on and here dollar sign and then is switched on  cool so hopefully you can see how this is working so get device state and if I scroll up in here  so you see that with our phone so we turn it off and here let's just say phone Dot and then get  and then device state so in here if I run this you should see that we have Apple iPhone is  on this is false right whereas so in here if I turn on the TV so 10 and then on and  then if I say TV DOT get and then device state run this we should see that if I scroll  up have a look Samsung Smart TV is on this is true awesome so this is pretty much how  you define properties and behaviors within your classes if you have any questions drop me a  message otherwise catch me on the next one okie dokie now the last thing that I want to show  you is Constructors when working with classes so you see that here we have our TV and the way  we initialize the values we say tv.brandtv.price the same for our phone Fondo brand phone.price  now it would be nice if when we actually create the object itself we were able to initialize  these values by passing them inside here well we can achieve this with Constructors so  let's scroll down to our blueprint so class and this is the smart device and in here  what we can do is we can say Constructor and then within this Constructor we can define  the properties so in our case we want brand as well as price and is switched on so I'm going  to put this on a new line so I'm going to press enter in here and let's have the brand so just say  brand and the type of it is string comma price the type of it is double and finally is switched  on so in fact let's just put everything under a new line and I'm going to say is switched  and then on and the type of it is a Boolean cool so now in here you see that we have the  Constructor and now we can pass the brand price and switched on so if I was to in here let's  just change the TV for now now in here you see that this is complaining because we need to pass  the value so here we just take this from here and here I'm gonna basically add a new line  and then paste that in there and also the price which was a thousand in here so a thousand and  whether it was on or off so what we're going to do let's just scroll down and let's have a default  value equals to I think what did we say we said false so false and you've learned about this  in here so this also works within Constructors and this is pretty much it so you can see  that now when we Define our TV we don't have to say tv.brandtv.price so we could just use the  Constructor itself which means that I can comment this out in here just like that and if I try to  run this so let's just go back in here and I'm going to add empty for now here so 0 0 and we'll  come back to this in a second because otherwise it's just complaining about it so if I run this in  here so what I want to see is that have a look we have 0.0 is switching on and then is on true but  really what we need is to say Samsung basically the name of it right and the reason why this  is doing this is because we are passing these values in here Samsung so for the brand and for  the price right but we're not assigning them to anywhere so what we have to do in this case is  two things so we could actually say right so the brand will be this brand so we just reassign  that and then for the price the same here and for the is switched on we can say is and then  switched on and if you want all together you can get rid of the type just like that so let's  just get rid of the type so it's not needed and just say equals cool now in here if I run this  now we basically assign the values can you see Samsung Smart TV it's now populated and we're good  to go or we have something even better so if I put my mouse in here it says property is explicitly  assigned to parameter brand so it can be declared directly in Constructor so what we can do is we  can get rid of the brand so let's just do for the brand first so we get rid of it and literally  it's just getting rid of it the same for the price in here and for switched on so we can move it to  Constructor and basically if I just undo this so you can see so what we're doing here is basically  the difference is that this in here becomes a variable inside of the Constructor so VAR VAR and  then the VAR okay so which means that now we can get rid of this and all the properties are within  the Constructor itself so if I run this you can see that this still works so Samsung Smart TV and  then this is the price is switching on is on true so if I hide this one other thing that I want to  show you is that you see that we have Constructor so this actually it's not needed so let's get  rid of it and it becomes much simpler so look how beautiful this code is now cool so that's pretty  much it you've learned about Constructors you've learned about the properties in here for the  objects and also the behaviors which are functions if you have any questions drop me a  message otherwise catch me on the next one oh cool you saw Constructors and  before you saw that we did add some random values in here for the  brand and price for our phone so what we want to do is the ability of having the  ability of using the Constructor in here like we did here but also have the ability of not even  passing something inside right so we want to have multiple Constructors if possible so the way to  do it in kotlin is the following so you can see that this is actually complaining but we have a  couple of things that we can do so if we want to we can basically say that basically these will  have a default value and the default value for these can be no so if I say equals to null in  here this complaints because we need to add the question mark so remember before so this is how  we handle nose so I can say equals to and then no now if I scroll up you can see that so we are able  to do this right so basically pass nothing inside so this is one technique or so let's just get  rid of this in here or what we can do is so let's just say basically like this what we  can do is have a secondary Constructor and we can have as many as we want so we can say  Constructor in here and basically if you want you can basically have you know variables again  and maybe you want a new variable for example or a new property Foo and you define the type string  for example and what we have to do here actually is be able to call the main Constructor and pass  these values in here so let's not do this for now and I'll show you in a second so here what we  do is we say colon in here and then say this and this pretty much refers to the main  Constructor and you can see that now we have to pass the price as well as the switched  on and the brand actually and here this is the point where we can basically I think if we say no  this will not work right because that cannot be null so we just pass empty Fields right so here  this will be 0.0 so this is another way in here and for example what's cool about this so let's  just scroll up you can see that here this works so what's cool about this is that we can have so  let's say that we want to have another Constructor where we want to be able to only pass the  brand for example right so here I can say VAR and then brand and let me put it on a new line  in a second so string so VAR brand just like this there we go and then we say this and we pass the  brand from this Constructor into the main one like so and it looks like we're not allowed to have VAR  that's fine on a secondary Constructor that's cool so we say brand and then string and then we pass  the brand inside which means that now in here I can basically remove the brand from here and then  just pass it within the Constructor so get rid of that and then here brand which is Apple iPhone and  hopefully now you can see how this is working out right so there we go so this is pretty much how  you can use multiple Constructors and also if you want these to be no so let's just say these can  be no so just add question mark in here for both price and brand right and if you want also for the  switch done in here just like that and with this it means that so here we could just say no and  here we could just also say no and obviously you see that we're not even using this Constructor  so IntelliJ is complaining about it but if I was to create a new device so here let's just say  device or smart device assign this to a variable so there we go Val and then I'm going to name this  as laptop for example there we go so you can see that we have a couple of Constructors one that we  don't pass anything another one that we only pass the brand and another one that we pass all the  fields brand as well as price and this is pretty much it and you can see also here we have default  right so defaults and uh yeah so if I run this everything should work as before have a look  Apple iPhone as well as the Samsung Smart TV qled cool this is pretty much everything on  multiple Constructors catch me on the next one now let's look into how can we get the  string representation of any object so I think before you saw that when we printed  the TV in here so if we print TV like so run you should see that we get a smart TV and then  at and then this random number which is the hash code so this really doesn't tells us anything and  more often what you want to do is the ability of printing the actual values I.E Smart TV the price  and all other attributes related to the object itself so instead of you saying Dot and then  brand and then Dot and then for example the price and whether is on I think right here so  instead of you doing all of this what we want to do is just the ability of so in here we  want to just print the object so just say print and we should get the exact same information for  that what we have to do is under our blueprint so smart device so this class which can be  found here let's go straight to the bottom and in here what we're going to do is let's right  click and then we're going to generate to string so two string is quite obvious on the name so  here we want to select all of these fields so brand price and is switched on basically all  the properties okay and this will actually override so override fun to string and this will  return the string representation for the object so here you can see that it says return and  then we have the brand price is switched on and we'll have all the fields Associated from  the generation screen that we just selected so now it means that if we  run this so if we run this we no longer should see the random string but  instead you can see that we have the class name then brand equals Smart TV price and all  the other fields cool so this is pretty much how you get the string representation  for your objects catch me on the next one let us now learn how to perform a quality  when we have our own classes and objects so in here we have this TV and let's  just leave it as TV for the name and let's say that we want to have the exact same  TV and we're going to call it TV and then two so TV1 and then TV2 now I want to know whether  these two televisions they are the same or these two smart devices are the same so the brand  is the same the price is the same so what we want to do is to check whether they are the  same so if I say print line and then TV One equals so double equals and then TV and then  two in here so if I run this this will give this false so you might be saying hold on these are the  exact same televisions so what is happening well when we perform this equality so equals and then  equal so 2 equals this is just saying whether TV1 refers to the same place in memory as TV2 which  obviously they are different right so TV1 is stored differently than TV2 however if I was  to change this so let's just get rid of that and I say TV2 equals to TV and then one in  here if I run this this now should gives us true because they refer to the same location  right so if you change TV1 TV2 will also change now let me go back in here and leave this as  is now in quote link things work a little bit different and that is we have the triple equality  so in here equals equals and then equals so three equals and basically this is used to check the  reference so whether these two refer to the same place in memory so if I run this this will  be false in here and if I change this to TV1 this will be true right now when this actually  comes into play is so you saw that either this or triple equals this is the same however if we  want to check whether the contents of these two objects are the same right so before we had so in  here we had TV2 with the exact same contents here the brand is the same the same for the price so  if we want to perform this equality we use this equals in here and what we have to do is under  our blueprint we have to override the equals and hash code so literally right after two string  right click and go to generate and here equals in hash code so again select all members in  here leave everything checked and then create now what this is actually doing is basically  performing the equality based on all Fields so first is actually checking whether they  refer to the same place in memory and here have a look triple equals so this refers to the  same place in memory right and then if this is the case then they are the same object then it  checks whether they are of different classes and if they're not then basically return  false otherwise it performs the casting and then here then we are comparing all  Fields so brand price as well as the Boolean cool so if I now scroll up and in here if we run  this this now should gives us true I've looked so before without the equals and two string this was  giving us false but now it's behaving correctly also if I was to say triple equals so in here  let's just say double quotes on both sides and here and what I want to do is I want to say  equals in here and then dollar sign curly bracket and end curly bracket on this side in here  and let's do the same for this so this will be triple equals and then dollar sign curly bracket  and then close curly bracket on this side with double quotes cool and here let's just have triple  equal so if you run this now you can see that are they equal yes because we did override  the equals in hash code and are they equal in memory so this is actually comparing the memory  location okay let me just add a comment memory location so run once more and you can see that  this is true because all the fields are the same and in here this will return false because  they don't refer to the same memory location awesome if I scroll up or down actually so  you see that we have the equals but also hash code now this in here has to do when  we are dealing with hash Maps so let's not focus about this and we'll look into this  later but for now this is pretty much it so just to prove a point if I was 2 in here  change for example these two Samsung and then TV for example now when we perform this right here  so are they equal this will be false because brand for TV2 is different than brand for TV1 and  they don't point to the same memory so if I was to run this this will be false and then  false I will look false and also false awesome and this is how you perform equality on objects  so I'm going to revert this so you have it for reference if you have any questions drop me  a message otherwise catch me on the next one as you can see kotlin it's a powerful and  beautiful language if you enjoyed this video literally just take one second and smash the like  button also if you haven't subscribed do so and as I said this is part of the massive course  that I'm planning for kotlin so head over to the website and stay up to date with the latest  recordings and also give me some suggestions for what you want to see on kotlin but you'll see  the list of topics which I've already planned and in case you have any other ideas I would like to  hear from you this is pretty much it comment down below let me know what other videos that you want  to see next and I'll catch you on the next one thank you

Channel: Amigoscode

Views: 125,257

Keywords: kotlin, kotlin tutorial, kotlin tutorial for beginners, kotlin full course, kotlin full tutorial, kotlin android tutorial, jvm, kotlin vs java

Id: TEXaoSC_8lQ

Length: 294min 12sec (17652 seconds)

Published: Mon Jun 26 2023