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.
