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

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Q31. Write a Program to find the middle element of Linked List ?

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Q32. How can we get an array out of ArrayList ?

Core Java

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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Q33. What is the trade off between using Collections.synchronizedList() on an ArrayList and a CopyOnWriteArrayList?

Core Java

Ans. Synchronized List locks the whole list to provide synchronization and thread safety during the read or write operation, while, CopyOnWriteArrayList doesn’t lock the whole list during these operations.
The CopyOnWriteArrayList class works according to its name i.e. copy-on-write which performs different actions for reading and write operations. For every write operation (add, set, remove, etc), it makes a new copy of the elements in the list. and for the read operations (get, iterator, listIterator, etc), it works on a different copy. So there is no additional overhead during a read operation and its read operation is faster than Collections.SynchronizedList(). Thus, COWAL is better for reading operation than Synchronized List.

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Q34. why aren't arrays better than array list ?

Core Java

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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Q35. Why iterators of an array list are fail fast ?

Core Java

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

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Q36. What problem we could have with ArrayList which aren't possible with Vectors ?

Core Java

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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Q37. What is the quickest way to find count of duplicate elements in an arraylist, without using iteration or loops ?

Core Java

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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Q38. What does the following initialization mean ?

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

What could be the use of such a collection.

Core Java

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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Q39. Which of the two - Arrays or LinkedList - is a better data structure for implementing Queue ? and Why ?

Data Structure

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Q40. How is LinkedList collection class internally implemented ? Is it a Linked List or Doubly Linked List ?

Core Java

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Q41. What are the ways to get the values from list ?

Data Structure

Ans. list.get(index);

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Q42. When do you use a Vector?

Core Java

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Q43. Can we modify a list while iterating it ?

Core Java

Ans. No,we cannot.I t will give concurrentModificationExceptin error. It can be resolved by using ConcurrentClasses like ConcurrentHashMap,CopyOnWriteArrayList,BlockingQueue etc which are fail-safe and wont give exception.

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Q44. Which of the following - arrays or LinkedList allow elements to be accessed using index and how ?

Data Structure

Ans. Arrays allows elements to be accessed directly using the index.

As Array elements are stored in continuous memory locations it's very easy to find the memory address of any element using the formula as following

Memory Address of Array start or index 0 + ( Size of array element * Index )

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Q45. Write code to see if a Linked List has cycle in it ?

or

Write code using Floyd Algorithm to see if a linked list has cycle in it ? What is it's comlexity ?

Algorithm

Ans. public class LinkedList {

Node start = null;
Node head = null;

class Node {
Integer body;
Node nextNode;

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

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

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

ll.traverse();

if(checkIfLoop(l1)){
System.out.println("There is a Loop");
} else {
System.out.println("No Loop");
}
}

private boolean checkifLoop(Test l1) {
Node slow = start;
Node fast = start;
Node faster = start;

while(slow != null ) {
fast = slow.nextNode;
faster = fast.nextNode;
if(slow == fast || slow == faster) {
return true;
}
slow = slow.nextNode;
}

return false;
}

}

Complexity of this algorithm is O(n)

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Q46. What can we do if we need to retrieve Fibonacci value at a particular index faster ? Can we use Linked List ?

Data Structure

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Q47. Difference between Arrays and LinkedList ?

Data Structure

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Q48. Detect a loop in a linked list

Data Structure

Ans. Work with two pointers on the linked list - a slow pointer (increments by one node) and a fast pointer (increments by two nodes). If both of these pointers meet at the same node, then there is a cycle in the linked list. Otherwise, no cycle.

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Q49. Difference between List and ArrayList ?

Core Java

Ans. List is an interface whereas ArrayList is an implementation of List.

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Q50. What is the default size of list ? How it is growable ?

Core Java

Ans. Default size is 10.
Regard how size will increase.

Inside add() method there is one method called ensureCapacity() which will check list has enough size available.

This ensureCapacity() method if found size of list need to increase then it will call grow() method which will create new list of extra size and copy existing list data to new one and return.

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Q51. difference between ArrayList and array ?

Core Java

Ans. ArrayList is a variable length collection class whereas arrays are fixed length primitive structure.

We can use generics with arraylist but not with arrays.

We can store primitive data types within arrays but can't with ArrayList. In ArrayList that needs to be converted to Wrapper objects.

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Q52. Difference between ArrayList and HashSet ?

Core Java

Ans. ArrayList is a list , i.e an implementation of List interface whereas HashSet is a Set and an implementation of Set interface.

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Q53. How can we create an arraylist of unique values ?

Core Java

Ans. We can put the value in a set to enforce uniqueness and then dum those value into an arraylist.

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Q54. What is the difference between closing and completing the observer / listener ?

Angular

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Q55. What will be the output of exceuting main method ?

public static void main(String[] args){
      List list = new ArrayList();
      list.add(1);
      list.add(2);
      list.add(3);
      System.out.println(list);
   }

Core Java

a. 1,2,3

b. Order cannot be determined

c. compilation error

d. 3,2,1

Ans.a. 1,2,3

Q56. What will be the output of this code

ArrayList list = new LinkedList();
list.add(3);
list.add(2);
list.add(1);
System.out.println(list);

Core Java

a. 1,2,3

b. 3,2,1

c. Order cannot be determined

d. Compilation Error

Ans.d. Compilation Error

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