Collection

Collection Hierarchy in Java

Why Map interface doesn't extend Collection interface? 

Why set interface doesn't allows duplicates in Java?

Why TreeSet does not allow null value in Java?

UnsupportedOperationException when adding or removing element to a Collection in java

How HashMap works internally in Java? 

Internal Implementation of TreeMap in Java  

Internal implementation of ArrayList in Java  

Internal Implementation of LinkedList in Java

Difference between HashSet and TreeSet in Java

Difference between fail-safe and fail-fast iterator in Java

Java Program to Reverse a Linked List using Recursion and Loops 

Difference between HashMap and Hashtable in collection in Java  

How to Remove duplicates from ArrayList in Java

How to iterate the TreeMap in reverse order in Java 

Example to sort keys of TreeMap using Comparator with Custom Object  

Java Program to Count Occurrence of Word in a Sentence  

Collection Related Interview Questions and Answers in Java(List,Map & Set)