Collections

Question 1

Which invocation of the remove(some args) method throws Exception?

Answer 1

Eg.., remove(100). If the list doesnt contains 100 elements, this invocation throws IndexOutOfBoundException

remove(object), if that object doesnt exists, returns false instead of throwing an exception

Question 2

For which purposes ArrayList is very good?

Answer 2

Lookup of element at constant time.

Adding or removing of element is slower than accessing the element

Question 3

What is LinkedList?

Answer 3

It implements both List and Queue.

Question 4

Main benefit of LinkedList?

Answer 4

access, add or remove element from both the beginning and end of the list

Question 5

Which classes does the Stack extends?

Answer 5

Stack extends Vector

Question 6

Treeset implement which Set other than Set?

Answer 6

NavigableSet interface

Question 7

What are the methods that NavigableSet interface provides?

Answer 7

lower(E e), floor(E e), ceiling(E e), higher(E e)

Question 8

When do we use Queue?

Answer 8

When we want element to be added or removed in specified order

Question 9

What is special about double-endede Queue?

Answer 9

We can insert/remove elements from both the front and back of the queue.

Question 10

What is ArrayDeque?

Answer 10

It is a pure double-ended Queue.

It stores its element in resizeable array

Question 11

The methods that are available in the ArrayDeque and used in stack are?

Answer 11

push, peek, pop

Question 12

What is HashMap?

Answer 12

HashMap stores the key in hash tables. This means that it uses hashCode() method of keys to retrieve their values more efficiently

Question 13

Treemap

Answer 13

Stores the Key in sorted tree structure

Question 14

How to get a set of all keys in a map?

Answer 14

calling keySet()

Question 15

How to get collection of all values?

Answer 15

values()

Question 16

Can we call contains on the Map interface?

Answer 16

No, contains is on the Collection interface and cannot be called here

Question 17

Can TreeSet allow null?

Answer 17

No, Tree Set involves sorting of elements and object cannot be null for sorting purposes

Question 18

What is interesting about null in TreeMap?

Answer 18

It allows null values, but no null keys

Question 19

What is to note about null in Arraydeque?

Answer 19

We cannot put null in ArrayDeque. Some method(poll)

return null as value sometimes and we cannot have null in the collection of ArrayDeque

Question 20

Which Map doesnt allow null keys or values?

Answer 20

Hashtable

Question 21

What are the collections that does not allows null?

Answer 21

1. Hashtable - no null values
2. TreeMap - no null Keys
3. TreeSet - no null values
4. ArrayDeque -no null values