HashMap Implementation notes

Implements Map interface

Permits null values and null key

None of the methods of HashMap are synchronized, so if you are adding or deleting keys - you must synchronize in multi threaded environment. Synchronize on some object, if  external object is not available use Collections.synchronizedMap(new HashMap())

Collections.synchronizedMap(new HashMap()) synchronizes all map operations using a internal mutex. However synchronization every single method is not enough, some client side locking is also required.

Iterators of HashMap are fail-fast when underlying map is modified (add/delete key) - ConcurrentModificationException is thrown.

Ordering of keys is not guaranteed to be same over time.

Access for get and put is time constant.

Max Capacity ~ 1.07 billiion

Default Initial capacity = 16

Uses hash function to disperse keys around.--

Uses Array to store elements.

Try and provide capacity  as part of initialization.