How HashMap works in Java

How HashMap  works in Java
HashMap  works on principle of hashing, we have put() and get() method for storing and retrieving object form HashMap .When we pass an both key and value to put() method to store on HashMap , it uses key object hashcode() method to calculate hashcode and they by applying hashing on that hashcode it identifies bucket location for storing value object. While retrieving it uses key object equals method to find out correct key value pair and return value object associated with that key. HashMap  uses linked list in case of collision and object will be stored in next node of linked list.
Also HashMap  stores both key+value tuple in every node of linked list.

What will happen if two different HashMap  key objects have same hashcode?
They will be stored in same bucket but no next node of linked list. And keys equals () method will be used to identify correct key value pair in HashMap .

In terms of usage Java HashMap is very versatile and I have mostly used HashMap as cache in electronic trading application I have worked . Since finance domain used Java heavily and due to performance reason we need caching HashMap and ConcurrentHashMap  comes as very handy there. You can also check following articles form