Java Collection Framework

Here are 10 essential multiple-choice questions on Java Collection Framework, covering key concepts

Last Updated : Apr 1, 2025

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Question 1

Which of the following is NOT a part of the Java Collection Framework?

A
Map
B
Queue
C
Array
D
Set

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Question 2

What will be the output of the following code?

Java

import java.util.*;
public class Test {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>();
        list.add("A"); list.add("B"); list.add("C");
        Collections.reverse(list);
        System.out.println(list);
    }
}

A
[A, B, C]
B
[C, B, A]
C
Compilation Error
D
Runtime Error

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Question 3

Which interface extends Collection but does NOT allow duplicate elements?

A
List
B
Queue
C
Set
D
Map

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Question 4

Which method in the Collections class is used to make a collection immutable?

A
Collections.lock()
B
Collections.unmodifiableCollection()
C
Collections.freeze()
D
Collections.readOnlyCollection()

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Question 5

What will happen if you try to add a null key in a HashMap?

A
Throws NullPointerException
B
Allowed only if the value is non-null
C
Allowed, but only once
D
Allowed multiple times

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Question 6

Which of the following is true about LinkedHashSet?

A
It allows duplicate elements
B
It maintains insertion order
C
It sorts elements in ascending order
D
It does not use hashing

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Question 7

What is the default capacity of ArrayList when using the no-arg constructor?

A
0
B
10
C
16
D
1

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Question 8

What will be the output of the following code?

Java

import java.util.*;
public class Test {
    public static void main(String[] args) {
        List<Integer> list = Arrays.asList(1, 2, 3, 4);
        Collections.fill(list, 5);
        System.out.println(list);
    }
}

A
[1, 2, 3, 4]
B
[5, 5, 5, 5]
C
Compilation Error
D
Runtime Error

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Question 9

Which of the following Queue implementations provides thread-safe access?

A
LinkedList
B
PriorityQueue
C
ArrayDeque
D
ConcurrentLinkedQueue

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Question 10

What is the key difference between Collection and Collections?

A
Collection is a class, while Collections is an interface
B
Collection is an interface, while Collections is a utility class
C
Both are interfaces
D
Both are utility classes

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