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Core Java - Interview Questions and Answers for 'List' - 47 question(s) found - Order By Newest

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Frequently asked.
 Q1. If you are given a choice to use either ArrayList and LinkedList, Which one would you use and Why ?Core Java
Admin
info@buggybread.com
Ans. ArrayList are implemented in memory as arrays and hence allows fast retrieval through indices but are costly if new elements are to be inserted in between other elements. LinkedList allows for constant-time insertions or removals using iterators, but only sequential access of elements

1. Retrieval - If Elements are to be retrieved sequentially only, Linked List is preferred.

2. Insertion - If new Elements are to be inserted in between other elements , Linked List is preferred.

3. Search - Binary Search and other optimized way of searching is not possible on Linked List.

4. Sorting - Initial sorting could be pain but lateral addition of elements in a sorted list is good with linked list.

5. Adding Elements - If sufficiently large elements needs to be added very frequently ,Linked List is preferable as elements don't need consecutive memory location.

  Sample Code for ArrayList

  Sample Code for LinkedList

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Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.
  Q2. What is the difference between ArrayList and LinkedList ?Core Java
admin
info@buggybread.com
Ans. Underlying data structure for ArrayList is Array whereas LinkedList is the linked list and hence have following differences -

1. ArrayList needs continuous memory locations and hence need to be moved to a bigger space if new elements are to be added to a filled array which is not required for LinkedList.

2. Removal and Insertion at specific place in ArrayList requires moving all elements and hence leads to O(n) insertions and removal whereas its constant O(1) for LinkedList.

3. Random access using index in ArrayList is faster than LinkedList which requires traversing the complete list through references.

4. Though Linear Search takes Similar Time for both, Binary Search using LinkedList requires creating new Model called Binary Search Tree which is slower but offers constant time insertion and deletion.

5. For a set of integers you want to sort using quicksort, it's probably faster to use an array; for a set of large structures you want to sort using selection sort, a linked list will be faster.

  Sample Code for ArrayList

  Sample Code for LinkedList

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 Q3. In a Linked list with sorted numbers, insert a new numbers while maintaining the sort order.Algorithm2017-07-25 14:59:01

Ans.
public class LinkedList {

   Node start = null;
   Node head = null;
   
   class Node{
      Integer body;
      Node nextNode;
      
      Node(Integer value){
         body = value;
      }
   }
   
   private void insertInMiddle(Integer value){
      head = start;
      if(start == null) {
         start = new Node(value);
         head = start;
         head.nextNode = null;
         return;
      }
      
      while(head.body < value){
         if(head.nextNode == null || head.nextNode.body >= value){
            Node newNode = new Node(value);
            newNode.nextNode = head.nextNode;
            head.nextNode = newNode;
            
            break;
         }   
         head = head.nextNode;
      }
   }
   
   private void traverse(){
      head = start;
      while(head != null){
         System.out.println(head.body);
         head = head.nextNode;
      }
   }
   
   public static void main(String[] args){
      LinkedList ll = new LinkedList();
      
      ll.insertInMiddle(5);
      ll.insertInMiddle(10);
      ll.insertInMiddle(15);
      ll.insertInMiddle(7);
      
      ll.traverse();
      
   }
}

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Frequently asked in Tech Mahindra ( Based on 3 inputs )
  Q4. What is the difference between List, Set and Map ?Core Java
Anonymous
Ans. List - Members are stored in sequence in memory and can be accessed through index.
Set - There is no relevance of sequence and index. Sets doesn't contain duplicates whereas multiset can have duplicates.
Map - Contains Key , Value pairs.

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  Q5. Difference between Vector and ArrayList ?Core Java
Anonymous
Ans. Vectors are synchronized whereas Array lists are not.

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 Q6. Will this code give error if i try to add two heterogeneous elements in the arraylist. ? and Why ?

List list1 = new ArrayList<>();
list1.add(5);
list1.add("5");
Admin
info@buggybread.com
Ans. If we don't declare the list to be of specific type, it treats it as list of objects.

int 1 is auto boxed to Integer and "1" is String and hence both are objects.

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 Q7. Difference between ArrayList and LinkedList ?
Admin
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Ans. LinkedList and ArrayList are two different implementations of the List interface. LinkedList implements it with a doubly-linked list. ArrayList implements it with a dynamically resizing array.

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 Q8. Find the third last element in a linked list ?Data Structure2017-03-27 08:53:16

 This question was recently asked at 'Compro Technologies'.This question is still unanswered. Can you please provide an answer.


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 Q9. Write a program for LinkedList, with method to append node and traversing the list ?Algorithm2017-07-25 14:31:33

Ans. public class LinkedList {

   Node start = null;
   Node head = null;

   class Node {
      Integer body;
      Node nextNode;

      Node(Integer value) {
         body = value;
      }
   }

   private void addNodeToEnd(Integer value) {
      if (start == null) {
         start = new Node(value);
         head = start;
         head.nextNode = null;
         return;
      }

      while (head.nextNode != null) {
         head = head.nextNode;
      }

      head.nextNode = new Node(value);
   }

   private void traverse() {
      head = start;
      while (head != null) {
         System.out.println(head.body);
         head = head.nextNode;
      }
   }

   public static void main(String[] args) {
      LinkedList ll = new LinkedList();

      ll.addNodeToEnd(5);
      ll.addNodeToEnd(10);
      ll.addNodeToEnd(15);

      ll.traverse();

   }
}

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 Q10. Write method to delete Node from a LinkedList.Data Structure2017-07-25 15:09:59

Ans. public class LinkedList {

   Node start = null;
   Node head = null;

   class Node {
      Integer body;
      Node nextNode;

      Node(Integer value) {
         body = value;
      }
   }

   private void addNodeToEnd(Integer value) {
      if (start == null) {
         start = new Node(value);
         head = start;
         head.nextNode = null;
         return;
      }

      while (head.nextNode != null) {
         head = head.nextNode;
      }

      head.nextNode = new Node(value);
   }
   
   private void deleteNode(Integer value) {
      head = start;
      while (head.nextNode != null) {
         if(head.nextNode.body == value){
            head.nextNode = head.nextNode.nextNode;
         }
         
         head = head.nextNode;
      }
   }
   
   

   private void traverse() {
      head = start;
      while (head != null) {
         System.out.println(head.body);
         head = head.nextNode;
      }
   }

   public static void main(String[] args) {
      LinkedList ll = new LinkedList();

      ll.addNodeToEnd(5);
      ll.addNodeToEnd(10);
      ll.addNodeToEnd(15);

      ll.traverse();
      
      ll.deleteNode(10);
      
      ll.traverse();

   }
}

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 Q11. Example of Observer Design Pattern ?
Anonymous
Ans. Listeners.

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 Q12. What is a Listener ?Design
Anonymous
Ans. In GUI programming, an object that can be registered to be notified when events of some given type occur. The object is said to listener? for the events.

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 Q13. Is it legal to initialize List like this ?


LinkedList l=new LinkedList();
Admin
info@buggybread.com
Ans. No, Generic parameters cannot be primitives.

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 Q14. Which of the following syntax are correct ?a. LinkedList<Integer> l=new LinkedList<int>();b. List<Integer> l=new LinkedList<int>();c. LinkedList<Integer> l=new LinkedList<Integer>();d. List<Integer> l = new LinkedList<Integer>();Core Java
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Ans. All are correct.

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 Q15. What is CopyOnWriteArrayList ?
Admin
info@buggybread.com
Ans. Its a type of ArrayList in which all Write operations , i.e add and set are performed by creating a new copy. This array never changes during the lifetime of the iterator, so it never throws ConcurrentModificationException

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 Q16. What are the advantages and disadvantages of CopyOnWriteArrayList ?Core Java
Admin
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Ans. This collections class has been implemented in such a manner that it can never throw ConcurrentModificationException. As it performs update and write operations by creating a new copy of ArrayList, It's slower compared to ArrayList.

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 Q17. Name few classes that implement List interface ?
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Ans. http://www.buggybread.com/2015/02/java-collections-classes-that-implement_35.html

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 Q18. What will the following code result ?

List> intList = new ArrayList>();

intList.add(Optional.empty());
intList.add(Optional.of(2));
intList.add(Optional.of(3));
intList.add(Optional.of(4));

System.out.println(intList.get(null));
admin
info@buggybread.com
Ans. Compile time error at last line as the get method expect argument of type native int.

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 Q19. What will the following code result ? Will it compile ?

List> intList = new ArrayList>();

intList.add(Optional.empty());
intList.add(Optional.of(2));
intList.add(Optional.of(3));
intList.add(Optional.of(4));

System.out.println(intList.get((Integer)null));
admin
info@buggybread.com
Ans. Yes but the last line will throw NullPointerException upon execution.

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 Q20. How to determine if the linked list has a cycle in it ?
admin
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Ans. http://stackoverflow.com/questions/494830/how-to-determine-if-a-linked-list-has-a-cycle-using-only-two-memory-locations

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 Q21. Can we add more elements to an array list that has been marked as final ?

Ans. Yes, the array list can hold more elements. Final only puts the restriction that the array list reference cannot hold any other array list.

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 Q22. Does an ArrayList allow elements of different types ? If not, Why the following code works List list1 = new ArrayList<>(); list1.add(1); list1.add("1");Core Java2016-07-29 11:44:07

Ans. With Java 7 or Later. If you don't declare the list to be of specific type , it treats it as list of objects. int 1 is auto boxed to Integer and "1" is String and hence both are objects.

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 Q23. Explain what happens when insertion is performed in case of ArrayList and LinkedList.Data Structure2017-10-26 15:52:53

Ans. Array List works on Array and when we add an element in middle of the list, Array List need to update the index of all subsequent elements. I the capacity is full, it even may need to move the whole list to a new memory location . Linked List works on Double linked list algorithm and all it has to do is to adjust the address of the previous and next elements.

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 Q24. What is the difference between Collections.emptyList() and creating new instance of List using new ?Core Java2016-10-25 10:35:08

Ans. But Collections.emptyList() returns an Immutable list whereas new arraylist() creates a mutable list.

Advantage of getting an empty list using Collections.emptyList is that it returns a singleton list which can be shared among many references and hence made immutable. This is good fit for situations where we would like to initialize a list to basic minimum empty to avoid null pointer exception.

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  Q25. Difference between Array and ArrayList ?Core Java2016-12-15 14:13:12

Ans. <a href="http://javahungry.blogspot.com/2015/03/difference-between-array-and-arraylist-in-java-example.html" rel="nofollow">http://javahungry.blogspot.com/2015/03/difference-between-array-and-arraylist-in-java-example.html</a>

  Sample Code for ArrayList

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 Q26. Write program to create a linked list and perform different operations on it.Algorithm2017-02-24 14:18:01

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 Q27. Write a Program to delete a node from Linked List ?Data Structure2017-05-25 08:22:58

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 Q28. Write a Program to find the middle element of Linked List ?Data Structure2017-03-27 08:39:28

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 Q29. How can we get an array out of ArrayList ?Core Java2017-05-07 16:42:41

Ans. We can get an array out of ArrayList by using toArray() method of an array list.

String a[] = arrayList.toArray();

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 Q30. What is the trade off between using Collections.synchronizedList() on an ArrayList and a CopyOnWriteArrayList?Core Java2017-05-07 19:31:54

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 Q31. why aren't arrays better than array list ?Core Java2017-05-31 11:42:53

Ans. 1. Arrays don't provide any built in support for sorting searching like operation and we need to do it explicitly.

2. It can hold only homogeneous objects,

3. We have to reserve memory as no dynamic expansion allowed.

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 Q32. Why iterators of an array list are fail fast ?Core Java2017-06-08 07:30:13

Ans. Because it's access isn't synchronized and hence access / modification by multiple threads may lead to inconsistent state.

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 Q33. What is meant by "Vector is synchronized and ArrayList isn't " ?Core Java2017-06-08 07:32:02

Ans. It means that only 1 thread can access have access to Vector at a time and no parallel access is allowed whereas Array List allows parallel access by multiple threads.

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 Q34. What problem we could have with ArrayList which aren't possible with Vectors ?Core Java2017-06-08 07:34:24

Ans. ArrayLists aren't synchronized and hence doesn't allow synchronized access. As multiple threads can access an arraylist in parallel, it may result in an inconsistent state.

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 Q35. What is the quickest way to find count of duplicate elements in an arraylist, without using iteration or loops ?Core Java2017-06-09 08:19:17

Ans. We can copy the elements to a Set and then find the difference of count between ArrayList and Set. As Set don't allow duplicates , they will be removed in the set.

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 Q36. What does the following initialization mean ?

ArrayList<LinkedList> traversalPaths = new ArrayList<LinkedList>();

What could be the use of such a collection.
Core Java2017-07-23 08:33:28

Ans. Initialize an ArrayList that will hold LinkedLists i.e every element of the arraylist will be a linked list.

Such collection could be used in algorithms that require first random access and then sequential traversal. For example - Storing traversal paths for a graph wherein we can start from any vertex. Implementing dictionary with each arraylist element holding staring with character and then linked list holding duplicate words.

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 Q37. Which of the two - Arrays or LinkedList - is a better data structure for implementing Queue ? and Why ?Data Structure2017-08-28 19:34:12

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 Q38. How is LinkedList collection class internally implemented ? Is it a Linked List or Doubly Linked List ? Core Java2017-08-28 19:40:39

 This question was recently asked at 'Ancestry'.This question is still unanswered. Can you please provide an answer.


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 Q39. What are the ways to get the values from list ?Data Structure2018-01-04 09:42:21

Ans. list.get(index);

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 Q40. When do you use a Vector?Core Java2018-01-22 17:32:25

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