SCJP Java Collections Framework

Question 1

Which Java collection class allows duplicate elements and maintains insertion order?

Accepted Answer

ArrayList

Answer

HashSet

Answer

TreeSet

Answer

LinkedHashSet

Question 2

Which interface does HashMap implement?

Accepted Answer

Map

Answer

List

Answer

Set

Answer

Queue

Question 3

What is the time complexity of retrieving an element from a HashMap by key (average case)?

Accepted Answer

O(1)

Answer

O(n)

Answer

O(log n)

Answer

O(n log n)

Question 4

Which collection maintains elements in a sorted natural order and does not allow duplicates?

Accepted Answer

TreeSet

Answer

ArrayList

Answer

LinkedList

Answer

ArrayDeque

Question 5

What happens when you add a duplicate key to a HashMap?

Accepted Answer

The old value is replaced by the new value

Answer

An exception is thrown

Answer

The old value is retained and the new one is discarded

Answer

Both values are stored under the same key

Question 6

Which of the following is NOT part of the Java Collections Framework hierarchy?

Accepted Answer

Array

Answer

List

Answer

Set

Answer

Map