Java Collections Interview Questions and Answers - New Version

welcome back and welcome to this all-important topic of collections what we look at in this section is collections what are the important interfaces which are present in the collection interfaces what are the important classes which are present in the collection hierarchy and how are they different what collection do you want to use in what scenario those are the kinds of things that we would want discuss as part of this section so let's start with the basic question why do we need collections in Java the fact is the basic data structure in Java array it's not really dynamic in the sense that once you create an array you cannot really expand the size of it so you cannot create an array of five and make it an array of size six no that's not possible so once you have defined an array the size of the array would remain the same throughout if you want to add an element to already full array what you need to do is create a new array of a bigger size copy the elements to it and add the new element so that's the only way you can add things to an array there is definitely a need for a data structure which is more dynamic and that's where the collections come in collections allow to add element delete an element and a lot of other operations and there are a number of collections which are present in Java a few of which we would look as part of the next videos in this section the approach we will take in this in this section is we will understand the interfaces and the classes so at a high level first we would start with the important interfaces we would understand them in depth and then go into these specific classes so what are the important interfaces in the collection hierarchy interfaces are very important because they define what is allowed what are the operations that are allowed and based on which you can actually set constraints for the implementations with basic interfaces which are the basic interface is collection so that is the base collection I am a base interface for all classes in the collection hierarchy it is collection the set interface extends collection so is the list interface however the set interface only allows unique things it does not allow duplication so any implementation of the set interface should not have duplication so I should not have the same element present twice however in a list it is a position based thing so you can have the same element present multiple times so set is all about unique things so it does not allow duplication whereas list is about a list of things it does not worry if that duplicates or not it only cares about the position each object is in if you look at a list it has methods which allow adding elements by specific position or you can delete methyl image by a specific position or you can add elements without specific position in which case it is added at the end of the list the other important interface which is present in the collections interfaces and which extends the collection is queue interface queue however is to support an order of processing so let us say I have a list of things to do and I want to order them in the way I want to execute them then I would put them in a queue and I would start picking up the next one from the queue and I would start processing it so let us say I am its see I mean queues are used extensively everywhere right so I have a list of tasks to be processed through a program and they are in a queue and the queue allows us to pick up the topmost element process it and then pick the next element process it and next element and process it so that's basically a queue so until now we have seen three interfaces set list and queue all of these extents collection set is for duplicate I mean set is for unique elements list is for a list of things Q is more for a queueing kind of a scenario you want to pick up the earliest one and process it that kind of a scenario you would go for a queue the other interface which is present in the collections is map the most important thing about the map interface is the fact that it does not extend collection interface so even though map is considered to be part of the collections hierarchy collections general discussion about collections it does not extend a collection interface so the map is used to store key value pairs so at a key a I want to store five at kisi I have two so let's say I have a series of alphabets and I want to find out how many times each alphabet occurs so I can use alphabet as the key at the number of times it is present as the value so a is present five times C is present two times a map usually represents a key value pair kind of a thing so a key and a value and the key kinds of acts as a unique identifier those are the important interfaces in the collection hierarchy let's start with the collection interface and look at what are the methods that are defined in the collection interface so if you look at the collection interface the base methods which are in here are to add an element remove an element and you can add all from a collection remove all from a collection or retain only the things which are present in this collection other than that you can check if an object extension is present in a collection or if a set of objects are present in a collection and you have the standard methods size is empty and clear also you have an eye traitor which would enable you to loop around the collection the most important thing about the interface collection is that which all things extend collection set interface extends collection list interface extends collection queue interface extends collection so the set list and queue interfaces will also contain all the methods that are defined in here so set and list and queue also contain these methods so any taste way to remember what a specific collection supports is to remember the hierarchy of interfaces and watch each interface support so we looked at the collection interface collection interface basically supports adding an element checking event element exists adding a list adding a collection and removing things removing an object removing a collection I mean removing set of items from the collection other than the usual operations of size is empty and clear function so these all functions will also be supported by lists will also be supported by set and will also be supported by the queue interfaces so we'll discuss about the list interface next the list interface contains all the method from the collection interface because that's what it's extending other than the methods in the collection interface list supports getting a value and setting a value based on index so you can get a value at a specific index or you can set a value at a specific index or you can add at a specific index so those are all the kind of things index of a specific object last index of a specific object and a sublist saying I want the lists of items between this index and the next index those are the kinds of things that are present in the list interface so the collection interface basically supports adding an element removing an element adding a collection and things like that and the list interface supports in addition to that methods to add at a certain position position is an important thing in lists so the most important thing about the list interface is any implementation of the list interface would in maintain the insertion order what is insertion order so if I'm inserting an element a first and B next then in the list is always stored before B obviously this insertion order is only maintained if you don't use a specific position so if you just use add this element then it will always be before the element which is inserted after that let's switch over to the IDE and look at all the things which are present in here we are looking at a specific class called collection hierarchy it's income in 28 minutes our collections package so collection hierarchy I mean this is what we looked at earlier what are the important methods represent in the interface collection these are the important methods and next we started looking at the list so we looked at what are the important methods in the list interface we saw that there are a lot of additional methods but all these methods if you look at them they would have a position in them so in list the position is what is very important so a list of things cares about the position each object is in so the elements can be added in a specific position and also you can add elements without specifying position in case of that it will the element would be added at the end so we also saw that we can add different battement to the list and you can use indexing to remove the particular thing I mean particular battement so if you want to remove such in he's at index zero YouTube Batman dot removes zero or similarly I mean you can use an index to remove and index to get and also index to set the value so I am sitting batsman dot set to come up pointing so it would set the second element to pointing like it is in here so basically list is a collection where position is given a lot of importance the best example for list is the class ArrayList so the error list implements list it the access time in an ArrayList is very fast because the underlying data structure is an array so in an array you can easily access the element however insertion and deletion are very slow because insertion and deletion might need you to create a new array so you might need to copy stuff and things like that so insertion and deletion are really slow in an ArrayList compared to linker list the one important thing about ArrayList is that it is not thread safe so if you access the same array list instance from multiple threads the results might not be as you expect the other class which implements the list interface is the vector so vector is thread safe so all methods are synchronized so vector is basically a released with everything synchronized so if I just open up the vector clasp here I can open up vector from the java.util so I am opening Java util vector and you would see that all the methods in here are synchronized you can see it here so synchronized copy into synchronized trim to size synchronize synchronize you will see a lot of synchronized methods in here so synchronization is to prevent multiple threads to be able to access to the same instance at the same time so vector is exactly the same as an ArrayList except that is synchronized link list has elements linked to each other so they are doubly linked forward and backward to one another so linked list is an ideal choice as it says here to implement a stack or a queue because linked list also implements the queue interface so earlier we looked at the queue interface as so linked list implement both the list and the queue interface or the thing about linked lists is I trading through a list is little slower because you cannot directly access an element in the list you have to go through the sequence of elements and then access the specific thing however insertion and deletions would be faster because to insert something all that I need to do is change the link of the previous element to the element that you would want to insert and change the next link as well so it is very simple so it implements the queue interface so you can do a peak or a pole kind of thing to find out what is the next element in the queue until now we looked at list interface and we looked at a couple of implementations of the list interface ArrayList vector and linkedlist let us now move on to the set interface in this video let us look at set interfaces I mean the set interface and a few examples example implementations of the set interface the important thing about the set interface is that it does not allow duplication so if object 1 equals object 2 then only one of them can be in this set so as you can see there are not a lot of additional methods in the set interface or not a lot of additional important methods in the set interface compared to the collection interface so the exact methods in the collection interface are what are present in the set as well the only constraint the only additional constraint that set places in addition to the collections is the fact that you should not have any duplication in the elements in the list there are a couple more interfaces which are important in this set interfaces one is assaulted set interface and the other one is navigable set interface if you look at the sorted set interface the main difference between sortedset and set is sorting so what does the sorted set do it maintains elements in a salt tilled order so set interface does not guarantee any order but a sorted interface on the other hand keep the elements sorted so in addition to the usual methods that are supported in set it supports methods like subsets head set tail set so that's basically a sub set of elements between this value and this value and you can ask for head set and the tail set as well you can also ask for a first element and the last element because the elements are in an order you can specifically ask for a first element and a last element as well so that is the interface salted set the other interface which is present in in sets is the navigable set so navigable set actually extends the sorted set and it kinds of gives you additional navigation methods so it's a navigable set is nothing but a sorted set extended with navigation methods so it these navigation methods help you to find values which are close to something so let's say I want to find the nearest value which is lower than this or nearest value which is higher than this or you want to poll for the first element or poll for the last element this kind of things we would be able to get through the navigable set so the applicable set interface extends this ordered set interface so if you look at the hierarchy it's set sorted set extents set and navigable set extends sorted set the main important thing about set is elements in a set are always unique so sorted set elements are unique and they are in sorted order and navigable set provides a way I mean more navigation so it helps you to find elements which are lower than a specific element higher than a specific element or pole for a first and last element kind of stuff so that's the sorted set let us now look at a few implementations of set interface so the first thing which we will look at is the hash set so hash set implements set hash set does not guarantee ordering so anything that you see a word hash so if you see something like hash then that particular class will never support order of insertion so if I am inserting in xB order then the elements might be stored in any order ax BX ABB ax I mean there are number of orders that are possible so it might be stored in any specific order so hat set does not guarantee order hash set uses a kind of a hashing implementation the next set is link hash set one important about anything called linked is they would maintain the order of insertion so link hash set maintains the order of insertion has said does not maintain the order of insertion so if elements are inserted in order ax B the way of storing it in a link has set would be ax B as well that the main difference between a hash set and a link has set on the other hand a tree set implements set and navigable set and as we know navigable set extends the sorted set so basically tree set implements sets dead set and navigable set so the elements are stored in a sorted order so if I am inserting a CB the order of storing them would be a b c so it would be sorted stored in sorted order and it also has all the navigation methods that are implemented in navigable set so the three sets that we discuss right now or hasit link set and tree set in a hash set the order of insertion is not maintained but it would not store duplicate values just like any set so link has that on the other side maintains order of insertion and make sure that there are no duplicates and tree set does not maintain order of insertion but it stores then the elements in the sorted order and thereby you can use navigable set to find out a specific elements in a specific range or you can find out what is smaller than a current element what is bigger than a current element and all that kind of good stuff until now we looked at a few set interfaces there are three set interfaces basically the set sorted set and navigable set and we looked at three example said classes as well hash set linked hash set and reset at ab later point in this specific section we'll look at a few code examples for this as well but until then bye in this video let's look at the map interfaces and also get an issue of the different implementations so as we discussed earlier map supports key value pairs so for example I have a set of elements I want to store how many times each element is present so a is present five times C is present two times and so on and so forth so I use a as the key the element a as the key and the value is the number of times it is present so this kind of key value kind of a data structures fit the map structure so if you look at the map interface typically everything is a rounding everything is surrounding the key and the value kind of stuff so you have methods to check if there is a specific key there is a specific value you can get the value at a specific key and you can put key comma value so you can put something at this specific with this specific key and you can remove element having a specific key you can put all everything in another map you can do a clear the other things that you can see are around the key set so you can get the key set that's basically the set containing all the key values in the hash map or in the map actually so you can get a collection of values and also the entry set as well so this are the at the high level the important methods in the map interface the other important interface in the map hierarchy is this sorted map so sorted map as you can see extends map however sorted map would be storing the elements in the order of their keys so with a hash map I mean with a normal map ordering is not guaranteed but with a sorted map order of the elements is guaranteed so you can actually create I mean provide a comparator at the map creation time and sort the elements in the map according to that comparator as well so similar to the sorted set kind of a thing this also provides method like sub map headsman please tale map first key last key and things like that the elements are stored in the order of their keys so I can say I would want from this key to this key all the elements all the map elements I can create a sub map for that I can create also a head map or a tail map and also I can get the first key and the last key similar to the navigable set you have a navigable map so it's basically a sorted map extended with a few navigable method so you can get I want a key which is lower than this I want a key which is higher than this I want to keep which is at least as we guess this and so on and so forth let us look at a few sample implementations of the map so hash map implements map as with anything starting with hash ordering is not guaranteed so its hash map is unsalted unordered hash table on the other hand its synchronized so hash table is nothing but a synchronized hash map so if you open up the hash table class you would see synchronized on a lot of different methods other than that it's very similar to the hash map one difference between hash map and the hash table is the fact that a hash map allows a key with null value whereas hash table doesn't the other important hash map is the linked hash map with the linked hash map the insertion order is maintained linked cash map has slower insertion and deletion and you'd be able to iterate faster over all the elements the three map as you can see implements navigable map so all the elements in the three map are in sorted order and you can also use all the implement all the navigation methods which are present in the navigable map in this video our aim was to get a high-level overview of what are different interfaces and implementation classes which are present around the map interface until the next video bye let us now move into the Q&A today interfaces and classes the thing about Q is it extends collection as we already know so it puts supports all the collection elements Q is usually used for things like a processing kind of a thing so I want to store elements in the order I want to process them and I would want to be able to take the top element from the collection and process it those are the kinds of places where we use queues as you can see queue extends collection and it has a method to add so this is basically to add a element in to a queue this is to offer an element into the queue so this is basically similar to add basically we are adding an element into the queue also there is a remove method which is present in the queue which is basically used to retrieve and remove the head element so the top element on the queue will be returned back and removed Paul also does the same thing I mean it retrieves and removes the head of the queue but pole returns null if the queue is empty however if you look at remove method remove method would throw an exception if a queue is empty that is one thing you need to remember always use a pole if you do not want an exception so if you are okay with getting an exception then go ahead and use a remove method and P could return the element but it will not remove the element from the head of the queue a DQ is a double-ended queue that is basically it supports removing from both ends of the queue so you would be able to add at the first or added the last you can either offer first or offer last you can remove from first or remove from last so you can actually either do it from the front of the queue or from the back of the queue so Q is a basically DQ is a collection where you can actually insert elements at both sides of the queue and remove at both sides of the queue as well so this is what is called a double-ended queue the other important interface is the blocking queue so just to summarize whatever we have discussed until now as part of the queue we talked about the queue interface first and then we went into the double-ended queue interface and now we are looking at the blocking queue interface the blocking queue interface is used when when you want to support operations that wait for the queue to become non-empty so what does that mean so and I would want to get an element from the queue but the queue does not have any elements right now in that kind of situation I want to wait for an element to become available in those kind of situations we go for a blocking Q so interface blocking queue supports those kind of use cases so basically I am pulling a queue queue does not have any elements I would want to still wait for some time and wait for an element to be available interface blocking queue also has very similar methods as the queue interface except that it provides more constraints so first thing is add actually insert this specific element into the queue immediately but it throws an exception in case of a failure however if you look at the offer method it would return false in case of a failure and as expected there are offer methods with a specific wait period as well so you can say I want to add this element to the queue but I only want to wait for a specific time I do not want to wait infinitely so if there is no space on the queue return back so that's basically the specified wait time so if I am if I want to insert an element into the queue and the queue is full I do not want to wait forever so I am specifying a wait time so I am saying I would want to wait up to this time but no more the take L take method would wait until the element becomes available until the next element is available the take would wait for the element to be available the pole method on the other hand can take a time unit so it you can say I want to wait for this much time so I want to wait for this much time if there is no element available so I got to wait for two minutes if the element is not available not more basically we looked at three interfaces right so one is the Q which is kind of the base of all the Q interfaces Q you would want to store elements for processing and you have whenever you would want you can take the top element from the queue and process it so that's Q double ended queue is an extension of the queue in the sense that you can actually have insertion and removal at both the ends so you support inserting removing polling and everything at both ends and blocking queue extends the queue more for the use cases where I want to get the element from the queue but if the queue is empty I would want to be able to wait for certain amount of time so in those kind of scenarios I would go for a blocking queue now that we looked at the interfaces in the queue kind of collections we will now look at a few implementations the priority queue is one of the famous queues it implements the queue interface so basically in the priority queue the elements are sorted in the natural order so the elements are stored according to the ordering which is natural to them that's your priority queue every DQ on the other hand is a double-ended queue so I as you can see it here it implements a double-ended queue the array blocking queue implements blocking queue so it uses array as the data underlying data structure but you can wait for a certain period before an element becomes available the linked blocking queue on the other hand uses linked lists as the underlying data structure for blocking queue the thing about the link blocking queue is typically they have better performance than air a blocking queue but sometimes in very concurrent applications the performance is less predictable what we are trying to do in this video is try to get a overview of the queue interfaces and the queue implementations in one of the subsequent videos in this section we'll look at some of the code examples for these as well until the next video bye in the previous video we looked and collection interfaces and what are the different high level implementations that are present for each interface so we just got a high-level overview of entire collection classes in this video we look at a lot of examples sort of code examples around these collections let's start with a basic one the thing is even though I am doing an integers dot add 5 what I am doing is I am doing auto boxing so what happens here is auto boxing and it would create a new integer and put it into the list so collections can only hold objects they cannot hold primitives we are creating an ArrayList in here so we are creating a list ArrayList the way you add things into an ArrayList is using the add method so basically you can add without an index then the element is added at the end of the list so such in now draw it is added so draw it is added at the end of the list however I can add it a specific index as well so if I want to add it index 0 then what would happen such in would be pushed out and ganguly would be inserted at index 0 so if you add 0 comma ganguly then this is what would happen if you again add such in it would be added in because error list allows for duplicates like any other collection list also would support array lists would also support it contains method so you can take contain struggied it would return a true and you can I trait around the list using the iterator or the for loop the other methods which are present in the array list are index off so you can find where gravity is present so it returns true but in the previous list that we created there was no Bradman so if an element is not present it would return minus 1 you can also use index to get the element so if you can say I want the batchman at index 1 similar to an array the index for all the collections would start with 0 so the index runs from 0 to n minus 1 where n is the size or 0 to size minus 1 batchman dot get 1 would get the second element in the list so in the list that we had the second element is such so that's basically what is returned back and also there are two variations on the remove function you can either remove the element then it's directly removed and now if you have ganguly such insertion or you can remove the element at a specific index so I am saying remove element at index 1 so this such in which is at index 1 0 1 2 so index 1 is this so this is the one which is removed the other thing you can do is sort the collection so here I am saying collections dot sort numbers so this error list is sorted and 1 2 3 4 becomes 4 1 3 2 can you explain why this is because we are storing strings they are sorted in the alphabetical order of these strings I am clearly creating an array list with a cricketer class and I am trying to sort the I mean I am trying to print all the elements in there so the elements by default are in the insertion order so I inserted Brandon first such in next Dravid pointing so if I print cricketers here it would print the admin such in rabid and punting as we expected if the cricketer class does not implement the comparable interface so if the Creator class does not impair implement the comparable interface then I will not be able to use collections dot sort I will be only be able to use the sort function collection short function on any or any class that implements the comparable so here I am implementing the comparable enough now I can go ahead and because this is compared to is implemented I can use this I can do a sort around this so what we did was to make the collect cricketer class implement the comparable interface and then you'd be able to sort the cricketers so now they're sorted in the increasing order of their fronts Bradman 9 9 9 6 you can see that they're in the increasing order of their runs so collection dot sort should be used on any list of any items where the item implements the comparable interface the other option is also when you are creating when you are doing the sort you can actually provide a sorter so you can say I want to use a specific sort so how do we create a descending sorter is basically you implement the comparator and say you implement the comparator interface and implement a comparator of two instances of that particular object which is mentioned in here and then you can use this sorter to sort your cricketers as you can see the descending sorter sorts the batsman in the decreasing order of runs so such in comes first and Bradman comes last next let's look at a few examples of sets the sets the fact is that sets do not allow duplicates so let us take hasit and as we discussed earlier hasit does not implement any any suppress does not support ordering anything which starts with a hash if hash is the first four letters of a class then it would not support ordering so sim so hash it also does not support ordering so you can see here like I am implementing such in first I am adding such in first that could drive it next such in Druid I am again adding such in this would return false and because this is duplicate it will not be added in in a set you cannot store duplicates so you will not have such in Dravid such in nope it's just such in and Dravid because such an is a duplicate and next we are using a tree set in a tree set as we discussed earlier objects are stored in a sorted order so I am adding such in so it such in so Dravid drop it comes alphabetically before such in so table it would be first such in next Ganguly Ganguly alphabetically sits between Dravid and such int so that's the order in which they would be pleasant I am a triangle at searching again he is a duplicate so will not be added that's basically you were crease it so we looked at a couple of examples of set classes so hash set and reset next we would look at hash map so here I am creating a hash map with string and cricketer so the key is a string and the value is a cricketer the key I am using it as a name so name such in and D cricketers elect the Creator object so this is are storing elements into the hash map using the put put key comma value and I can do hash map gate pointing what does it do it gets the pointing element and it prints that to the output get Lara so Lara is not here so when I do a get when the key is not formed it would return a value null earlier pointing at 11,500 runs I am reusing the key here again and putting a new instance of the cricketer what happens is the existing instance existing pointing value gets overridden and this value would be replaced so if I do a hashmap gate pointing here it would be pointing 11800 whatever is the latest value that I put into the hash map tree map on the other hand is storing the keys in a sorted order so I am adding such in first so such in then I'm adding Dravid so draw it as a key is before such in so traveied such in mixed I'm adding pointing so P is between D and s so provide pointing such in and Bradman Bradman is first alphabetically so it comes alphabetically first so as you can see tree map stores the keys it stores the elements in the order of their keys next we have the navigable set and the navigable map interfaces right so tree set implements the navigable set interface tree map in elements the navigable map interface so as we discussed earlier tree set stores things in the sorted order so because the elements are in sorted order you can also navigate through them and try and get a set of things which are lower higher and things like that so the navigable map interface or the Navi will set interface has methods which allow us to do that so I am adding a set of elements into a tree set I am adding in a tree set five numbers so what you can do here is try and get elements lower than 25 so number to reseed dot lower than 25 how many are there just 1 5 I can also get the highest number which is lower than or equal to 25 how do you do that that is using the floor method you can get the lowest number that is higher than 25 so that is higher so which is the lowest number which is higher than 25 ceiling is the lowest number which is higher than or equal to 25 so here if you higher than 25 higher 25 it returns 35 so after 25 the next number is 35 on the other on the ceiling on the other hand also takes the element which you passed into consideration 25 is already an element in this so it would return 25 back and the same kind of things are possible with the treemap as well because treemap implements navigable map so you have a lower key floor key higher key and the ceiling key methods next we look at a few examples of the priority queue as we looked at it earlier priority queue stores elements in the order of their priority natural order so smaller numbers have higher priority natural ordering of numbers or small numbers have the higher priority so I am storing integers here so I am saying priority Q dot offer so I am offering a element into the queue so I am putting an element into this specific use 24 14 15 9 and 45 so if you print the priority queue you would see that it's storing elements in some random order it's not really in the priority order when I do a peek you can see that I get the element with the highest priority the one with the highest priority as we saw earlier is the smallest number which is 9 so I get 9 first the most important thing about the peek method is that it does not change the queue so the peak method just says the top element on the queue is 9 but I am NOT going to take it out of the queue so if you print the queue here it's still 9 24 15 and 45 however the pole method is a little different pole method would take the element out of the queue so when I do a pole it returns 9 but it 9 is now removed from the queue the remaining elements in the queue are 24 15 and 45 in the earlier priority queue what we did was we use the natural ordering but you can actually define a comparator which would give high priority to the biggest number so if you really want to create such a comparator you can do that and when you are creating the priority queue you can use a reverse comparator as well so that is one of the parameters that you can pass in to the priority queue constructor and now I can add elements to the queue and they would be removed if you do a peek now the highest element would come up so the highest element has the highest priority so that's your priority queue let us end this section by looking at a few static methods which are present in the collections class as we looked at as we discussed earlier collection is an interface collections is a class collections class has a lot of static methods some of them are in here you can do a binary search so you can pass a list as an input and you can do a binary search for a specific key and you can also do a binary search by passing a comparator in as well and you can reverse a list and also you can sort a list using these static methods which are present in the collections class so all the static methods which are present in the collections class are very useful to do operations on the collection objects one of the most important things about collections is that there are so many collections that it can get really confusing to remember whatever we are talking about so the best way I would suggest you to do is to take this collection hierarchy class and kind of take a printout or something of it and kind of look at it a few times this collection hierarchy class has all the important things that you need to remember about all the collection classes that we discussed and this collection examples class it's about 550 lines of code contains all the examples example pieces of code that we looked at in this particular section so I would really recommend you to do an exercise take 30 minutes spend some time looking at the collection hierarchy take a print out or something hang it somewhere and do whatever is in the collections examples at least once or twice try to go through it try to understand it in depth and I am sure if you complete these two examples you would be really thorough about whatever things that you need to know about Corrections until the next section bye-bye

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Keywords: in28minutes, Karanam, java interview questions and answers, java interview questions and answers for experienced, collection interview questions, Ranga, rithus, java collections interview questions, in28minutes tutorial, Java Collections Interview Questions and Answers, interview, collections interview questions, Collections Interview Questions and Answers, java interview questions, java, collection in java, Rao

Id: 3hgYHXDVh-o

Length: 43min 51sec (2631 seconds)

Published: Sun Sep 18 2016