java Collection Framework

Which method would you use to retrieve an element at a specific index in an ArrayList?

• get()
• indexOf()
• find()
• search()

Answer explanation

get() retrieves an element at the specified index in an ArrayList.

What happens when you add an element to an ArrayList at an index greater than its size?

• Throws an IndexOutOfBoundsException
• Resizes automatically
• Pads with null values
• Replaces the last element

Answer explanation

Adding at an invalid index throws an IndexOutOfBoundsException.

Which of the following operations are NOT supported by a Set?

• Adding duplicate elements
• Removing elements
• Iterating through elements
• Checking the size

Answer explanation

A Set does not allow adding duplicate elements.

True or False: A TreeSet maintains the insertion order of elements.

• True
• False
• N/A
• N/A

Answer explanation

A TreeSet orders elements naturally or via a comparator, not by insertion order.

Which method adds an element to the end of a Queue?

• add()
• offer()
• enqueue()
• insert()

Answer explanation

offer() is used to add an element to the end of a Queue.

Which collection allows adding and removing elements from both ends efficiently?

• LinkedList
• PriorityQueue
• ArrayList
• Deque

Answer explanation

Deque allows adding and removing elements from both ends efficiently.

What will happen if you try to retrieve an element from an empty PriorityQueue using remove()?

• Returns null
• Throws NoSuchElementException
• Throws IllegalStateException
• Adds a default element

Answer explanation

remove() throws NoSuchElementException if the queue is empty.

How can you synchronize a List in Java?

• Use Collections.synchronizedList()
• Use Vector
• Use LinkedList
• Both A and B

Answer explanation

Both Collections.synchronizedList() and Vector provide thread-safe List implementations.

Which of the following operations is fastest for an ArrayList?

• Adding at the beginning
• Adding at the end
• Removing the first element
• Removing the last element

Answer explanation

Adding at the end of an ArrayList is fastest due to dynamic array resizing.

What happens when you call poll() on an empty Queue?

• Returns null
• Throws an exception
• Resizes the queue
• Returns a default value

Answer explanation

poll() returns null if the queue is empty.