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# Java, C

## What is ArrayList (Java)?

ArrayList class extends AbstractList and implements the List interface.

ArrayList is a re-sizable array. In other words, it handles the resizing automatically. 

## What is Linked List(Java)?

LinkedList class extends AbstractSequentialList and implements the List, Deque and Queue interfaces.

## What is HashMap(Java)?

Hashmap extends AbstractMap to use a hash table.

 HashMap is non-synchronized

 HashMap allows one null key and multiple null values whereas Hashtable doesn’t allow any null key or value.