Java Constructor Tutorial - Learn Constructors in Java

if you're confused about constructors do not fret this video you're going to learn everything about constructors constructors are one of those big words that come with object-oriented programming the named constructor is kind of vague and a bit weird so I'm going to clear up any confusion you have today about constructors and by the end of this video you'll know exactly how to use them in your Java program I hope you're having a great morning afternoon or evening my name is Alex I make Java videos just like this every single week so if you're new here then consider subscribe let's hop in Eclipse go to file new Java projects I'll call it something like construction for constructors open it up and then create a new class inside of the source folder and we're going to call it shirts that's the kind of object we'll make today we'll make a shirt and to see what else is going on we'll right click on source again and make a main class which will have the main method which will let us run code inside of these curly braces so we can see what's going on so now we have main Java and shirt Java the word constructor is a lot like construction you see construction workers working on a building teachers will construct curriculums a construction worker makes a building a teacher makes a curriculum a constructor basically makes an object now let's recap what objects are everything in life are objects pretty much this mouse is an object this acoustic foam panel is an object which I'm going to put right behind my camera in a second my phone is an object everything so why do we have object oriented programming well if everything in the world is an object we can kind of program everything in the world inside of a computer hence object-oriented programming now an object in real life has certain properties and can do certain things so we represent objects in the computer as having certain properties and doing certain things so what are the properties of a shirt well for example the shirt I'm wearing it has a size and it has a color so to turn this physical shirt into an object in the computer let's add some properties well we can say it might have the property color so we can create a variable here called color and we're adding this private keyword so that only what's inside of the object knows what the color is don't worry too much about that right now if you're interested in about private and public keywords they're called Java access my fires you can learn more about those in a video on the screen now but our shirt has a color and it also has a size so we can create a char or something sighs those are the properties of this shirt now what are the things that this shirt can do well let's say you can put a shirt on you can take a shirt off so let's make some methods put on and I'll just print out shirt is on and take off take off a trick you can do with printing out is type sis out and then control space and that'll finish it for you pretty cool little trick I use sometimes so shirt is off so now our object has properties and things that it can do let's try to use the properties and things it can do inside of the main class and you'll start to see the importance of constructors so we come into the main class here to use this shirt we have to create this shirt so to create the shirt we type the name shirt we call it s equals new shirt this is how you create any object in Java and since shirt is in the same package it knows what it is so we don't have to add an import statement at the top or anything like that next to use things we type s dot and this brings up everything that the shirt can do and we can see put on and take off so let's put on the shirt save it and run it and we see shirt is on because when we click the green run-button we run code in here we create a shirt and we call s dot put on which goes in here and does this so before we said that constructors make objects and this line is how you make an object you say there's going to be a shirt object called s and it's going to be equal to a new shirt new shirt makes a new shirt so if this makes a new shirt and constructors make new objects then this should be the constructor and it is the constructor shirt is the default constructor which means this is how you make a shirt by default just like how the put on method has these parentheses the constructor also has parentheses because the constructor is basically a method that makes your object and all methods have parentheses after them so put on has parentheses and the constructor has parentheses and you might say well Alex put on is a method inside of this shirt class I see put on right here but I don't see shirt where is the shirt method it's not in here to make a constructor inside of your class you just type the name and then finish it off just like a method so if we print something out inside of here and then run it you'll see that when we create the shirt and call shirt it now thinks that this is the constructor and so it runs code inside of there but when this is gone then we use the default constructor which doesn't have any code in it it just makes makes it so this comes to the question well why would you ever want to make a constructor if you already have a default constructor which makes objects for you well you may want to create a shirt with say certain attributes so instead of making a shirt and then setting the color to white and then setting the sighs to medium you could say I want a shirt that's medium and way all at the same time so let's make our own constructor together I actually haven't used the color and size inside of methods yet but this would be as easy as saying set color color taking in a color and then saying color equals I'll call this new color new color will change these to static static and then doing the same thing for size set size new size new sighs sighs it should be a chart so if we use the default constructor this is what we would have to do we'd have to say a shirt equals shirt s dot set color to white and then s dot set size to M change these to public real quick so that we can see if you're following along that's a really good you will really start to see what's happening if you're following along here it'll make a constructor in a second but I really this is really important that we do this first so now we can see s dots color and s dot size save and run it now we can see white and M which is what we set through the shirt methods but this is kind of a lot if you just want to create a white medium shirt if you're creating a lot of objects very quickly and very often then you might not want to call set color or set size all the time you may want to just pass those in as parameters to the constructor and instead of saying hey give me a shirt and I'll do it myself I can just say give me a white medium shirt so let's do that let's destroy these and create a constructor so remember the constructor is just the name and then treat it like a method so the name here is shirt you say shirt and then treat it like a method this is the default constructor still so we really don't need to put anything in here we could even just not have it but this is here just so you can see it so we can make another constructor if we want to pass parameters so we can say shirt again just like before there's some red underlines because they're like yo this is the same code why do you have it twice well we're gonna pass in some parameters so we'll say we can pass in a color you could stop here you could just pass a color or you could add the size as well sighs if we save this and run it instead of using this constructor now we can use this one just like any method we see there's two parameters color and size so we'll just pass in those two parameters say white and and if we save it and run it we get null and that's kind of weird right well we called the constructor you say a shirt s equals new shirt with two parameters well I know there's a constructor with two parameters here so that's what we'll use but we're not actually doing anything with the color and size we're just passing it and then making an object we're not setting it so we got it set so we'll say that color equals the color and then the size equals the size and this is where it gets into well the name here is the same as the name up here there's a way to get around that using the this keyword but I'm just gonna change this to new color and new size and then replace that here okay so now if we save it and run it then we get white and so remember all the constructor does is it makes an object for you that's why if you create like a scanner scan equals new scanner this scanner I mean if we import it and everything inside the scanner class just like inside the shirt class it has a bunch of different constructors too so it has a scanner with a file that you pass into it a constructor scanner with the input stream all these so you can pass a path and a char set you could put a file and a string these are all constructors for a scanner so just like we have shirt it has a bunch of these that pass different parameters inside all the constructor does is make an object and you can have as many as you want and passing different things and yeah that's that's basically it if this was helpful please leave a like I've had a lot of requests to do this video on constructors in Java so yeah I'll see in the next video have a great day

Channel: Alex Lee

Views: 276,306

Rating: 4.9576521 out of 5

Keywords: java constructor, constructor in java, java constructors, java, constructor, constructors java, constructors in java tutorial, constructors in java for beginners, constructors java example, java constructor tutorial, how to use constructors in java, learn java, alex lee

Id: G1Iln3PSrUg

Length: 12min 25sec (745 seconds)

Published: Thu Oct 03 2019