Quiz Collections in Java

Which of these packages contain all the collection classes?

• java.lang
• java.util
• java.collections
• java.net

Which one of these interfaces does not extends Collection Interface?

• List
• Set
• Queue
• Map

Which of the following Statements are true about List Interface?

1. List indexes start from 0

2. List allows you to have 'null' elements

3. List allows you to have duplicate elements

4. List follows insertion order

5. List uses Hashing Algorithm

• 1,2,3,4,5
• 1,2,3,4
• 2,3,4,5
• 1,3,4

Which collection allows you to retrieve elements in the order they were inserted?

1. ArrayList

2. HashSet

3. LinkedList

4. LinkedHashMap

5. LinkedHashSet

6. TreeSet

• 1,2,3,4,5,6
• 1,2,3,4,5
• 1,3,4,5
• 1,4,5

Predict the output:

ArrayList<String> list = new ArrayList<>();

list.add("Java");

list.add("SQL");

System.out.println(list.remove(1));

• Java
• SQL
• true
• Compilation Error

Identify the classes which are synchronized and thread safe.

1. ArrayList

2. Vector

3. Stack

4. PriorityQueue

• 1,2,3,4
• 2,3,4
• 2,3
• 1,2,3

Which method removes all the elements from collection?

• clear()
• remove()
• removeAll()
• deleteAll()

Which collection class does not allows duplicate elements and maintains their insertion order?

• HashSet
• TreeSet
• LinkedHashSet
• HashMap

Which collection class stores objects in the form of key-value pairs?

• LinkedList
• LinkedHashSet
• LinkedHashMap
• LinkedTreeSet

Which method returns first element from a Queue without removing it?

• get()
• getFirst()
• peek()
• poll()