Core Java - Interview Questions and Answers for 'List' | Search Interview Question

Core Java - Interview Questions and Answers for 'List' - 54 question(s) found - Order By Newest

Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.

Q1. What is the difference between ArrayList and LinkedList ?

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

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve collections java data structures arraylist linkedlist arraylist vs linkedlist Asked in 61 Companies Basic frequent}

Try 1 Question(s) Test

Frequently asked.

Q2. If you are given a choice to use either ArrayList and LinkedList, Which one would you use and Why ?

Core Java

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

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java collections list arraylist linkedlist difference between architecture data structure ebay Asked in 2 Companies basic frequent}

Try 2 Question(s) Test

Q3. 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");

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.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java collections arraylist list autoboxing wrapper classes expert rare}

Q4. In a Linked list with sorted numbers, insert a new numbers while maintaining the sort order.

Algorithm

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();

   }
}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve LinkedList Data structures Algorithm}

Frequently asked in Indian Service Companies. Tech Mahindra ( Based on 3 inputs ) and Infosys ( 3 inputs )

Q5. What is the difference between List, Set and Map ?

or

What are the different Java Collections Interfaces ?

Core Java

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.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java collections list set map list vs set vs map Asked in 8 Companies basic frequent}

Try 1 Question(s) Test

Q6. Difference between Vector and ArrayList ?

Core Java

Ans. Vectors are synchronized whereas Array lists are not.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java basic interview question vector arraylist collections synchronization vector vs arraylist Asked in 35 Companies basic frequent}

Q7. Example of Observer Design Pattern ?

Ans. Listeners.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java design pattern listeners observer design pattern expert}

Q8. Difference between ArrayList and LinkedList ?

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.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java collections list arraylist linkedlist difference between basic frequent}

Q9. Find the third last element in a linked list ?

Data Structure

Ans. First Find the number of nodes in the linked list and take it as n.then find the data at n-3 element.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve linkedlist Asked in 1 Companies}

Q10. What is meant by "Vector is synchronized and ArrayList isn't " ?

Core Java

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.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve vectors arraylist collections list synchronization synchronized}

Q11. Write a program for LinkedList, with method to append node and traversing the list ?

Algorithm

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();

   }
}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve LinkedList Data structures Algorithm}

Q12. Write method to delete Node from a LinkedList.

Data Structure

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();

   }
}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve linkedlist delete node from linkedlist}

Q13. Difference between Arrays and ArrayList ?

Core Java

Ans. Both Arrays and ArrayLists are used to store elements. Elements can be either primitives or objects in case of Arrays, but only objects can be stored in Arraylist. Array is a fixed length data structure while arraylist is variable length collection class. Once created, you cannot change the size of the arrays, but arraylists can dynamically resize itself when needed.Another notable difference between Arrays and Arrayslist is that arary is part of core java programming and array list is part of collection classes

Sample Code for arrays arraylist

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve array arraylist array vs arraylist Asked in 7 Companies basic frequent}

Q14. Difference between List and LinkedList ?

Core Java

Ans. A List is an child interface of collection interface in java where as Linked list is and implementation class of List interface which has doubly linked as a underlying data structure

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve linkedlist list vs linkedlist Asked in 1 Companies}

Q15. What is a Listener ?

Design

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.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java gui ui programming swing awt swt listener architecture}

Q16. Is it legal to initialize List like this ?

LinkedList l=new LinkedList();

Ans. No, Generic parameters cannot be primitives.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java collections list linkedlist generics yes-no}

Q17. 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

Ans. All are correct.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java generics linkedlist list collections basic}

Q18. What is CopyOnWriteArrayList ?

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

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java collections list arraylist copyonwritearraylist ConcurrentModificationException Asked in 1 Companies}

Q19. What are the advantages and disadvantages of CopyOnWriteArrayList ?

Core Java

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.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java collections list arraylist copyonwritearraylist advantages-disadvantages ConcurrentModificationException Asked in 4 Companies Expert}

Q20. Name few classes that implement List interface ?

Ans. http://www.buggybread.com/2015/02/java-collections-classes-that-implement_35.html

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java collections list}

Q21. 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));

Ans. Compile time error at last line as the get method expect argument of type native int.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve arraylist list coding collections}

Q22. 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));

Ans. Yes but the last line will throw NullPointerException upon execution.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve collections arraylist list coding}

Q23. How to determine if the linked list has a cycle in it ?

Ans. http://stackoverflow.com/questions/494830/how-to-determine-if-a-linked-list-has-a-cycle-using-only-two-memory-locations

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve linked list data structure algorithm java ebay}

Q24. 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.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve ebay collections arraylist final keyword}

Q25. 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 Java

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.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve arraylist list collections}

Q26. Explain what happens when insertion is performed in case of ArrayList and LinkedList.

Data Structure

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.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve arraylist vs linkedlist collections list Asked in 2 Companies}

Q27. What is the difference between Collections.emptyList() and creating new instance of List using new ?

Core Java

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.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve collections Collections.emptyList immutable immutability immutability}

Q28. Difference between Array and ArrayList ?

Core Java

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

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve array arraylist Asked in 11 Companies basic frequent}

Q29. Write program to create a linked list and perform different operations on it.

Algorithm

Ans. import java.util.*;
class LinkedListSolution{
protected LinkedList list;
public LinkedListSolution(){
list = new LinkedList();
}
public Object pop() throws NoSuchElementException{
if(list.isEmpty())
throw new NoSuchElementException();
else
return list.removeFirst();
}
public void push(Object obj){
list.addFirst(obj);
}
public Object peek() throws NoSuchElementException{
if(list.isEmpty())
throw new NoSuchElementException();
else
return list.getFirst();
}
public boolean isEmpty(){
return list.isEmpty();
}
public String toString(){
return list.toString();
}
}
class TestStack{
public static void main(String args[]){
LinkedListSolution s = new LinkedListSolution();
s.push("First");
s.push("Second");
s.push("Third");
System.out.println("Top: " s.peek());
s.push("Fourth");
while(!(s.isEmpty()))
System.out.println(s.pop());
}
}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Linkedlist data structures algorithm Asked in 2 Companies basic}

Q30. Write a Program to delete a node from Linked List ?

Data Structure

^{This question was recently asked at 'Caprus IT'.This question is still unanswered. Can you please provide an answer.}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve linkedlist delete a node from linked list Asked in 1 Companies}

Search Interview Questions

Help us and Others Improve. Please let us know the questions asked in any of your previous interview.