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Java Iterators

Here are 10 essential multiple-choice questions on Java Iterators, covering key concepts.

Last Updated : Apr 3, 2025

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Question 1

What is the purpose of an Iterator in Java?

A
To modify elements in a collection
B
To traverse a collection one element at a time
C
To sort elements in a collection
D
To store elements in a collection

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Question 2

Which method of Iterator removes the last element returned by next()?

A
delete()
B
remove()
C
discard()
D
erase()

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Question 3

What happens if next() is called on an Iterator when there are no more elements?

A
It returns null
B
It resets the iterator
C
It throws a NoSuchElementException
D
It stops the iteration silently

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Question 4

Which type of Java collection supports ListIterator?

A
Set
B
Queue
C
Map
D
List

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Question 5

What is a key advantage of ListIterator over Iterator?

A
It can iterate in both forward and backward directions
B
It is faster than Iterator
C
It can modify the collection structure while iterating
D
It works with Set and Queue collections

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Question 6

What is the output of the following code?

Java

import java.util.*;

public class Geeks {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>(Arrays.asList("A", "B", "C"));
        Iterator<String> iterator = list.iterator();
        while(iterator.hasNext()) {
            System.out.print(iterator.next() + " ");
            iterator.remove();
        }
        System.out.println(list.isEmpty());
    }
}

A
A B C true
B
A B C false
C
A B C [A, B, C]
D
Compilation Error

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Question 7

Which of the following is NOT true about the Iterator interface in Java?

A
It allows removing elements during iteration
B
It works with Set, List, and Queue
C
It allows backward traversal using previous()
D
It provides hasNext() and next() methods

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Question 8

How can you safely modify a collection while iterating through it?

A
Using Iterator.remove()
B
Using List.remove(Object) inside a loop
C
Using collection.stream().forEach()
D
Using for-each loop

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Question 9

Which exception occurs when an Iterator is used after modifying the collection directly?

A
NullPointerException
B
ConcurrentModificationException
C
IndexOutOfBoundsException
D
IllegalArgumentException

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Question 10

What is the correct way to iterate over a HashSet?

Java

for (int i = 0; i < hashSet.size(); i++) {
    System.out.println(hashSet.get(i));
}

Java

Iterator<String> it = hashSet.iterator();
while (it.hasNext()) {
    System.out.println(it.next());
}

Java

for (String item : hashSet) {
    System.out.println(item);
}

D
Both B and C

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