Hashmap and Hashset in Java MCQs Exercise II

Ques 1 Hashmap and Hashset

Which of the following statements about HashMap is true?

A It allows duplicate keys.

B It allows null keys but not null values.

C It maintains the insertion order of elements.

D It is a synchronized class.

Ques 2 Hashmap and Hashset

Which of the following is not a method of the HashMap class?

A get()

B remove()

C contains()

D size()

Ques 3 Hashmap and Hashset

What is the time complexity of adding an element to a HashSet?

A O(1)

B O(n)

C O(log n)

D O(n log n)

Ques 4 Hashmap and Hashset

Which of the following is not a valid way to iterate over the key-value pairs of a HashMap?

A Using a for-each loop

B Using the values() method

C Using the keys() method

D Using an iterator

Ques 5 Hashmap and Hashset

What is the output of the following Java Code?

HashSet set = new HashSet<>();
set.add("Apple");
set.add("Banana");
set.add("Cherry");
System.out.println(set.isEmpty());

A true

B false

C Apple, Banana, Cherry

D Compilation error

Java Hashmap and Hashset Exercise