How HashMap works in Java ?

• The HashMap requires a hash function and uses hashCode and equals methods, in order to put and retrieve elements to and from the collection respectively. 
• When the put method is invoked, the HashMap calculates the hash value of the key and stores the pair in the appropriate index inside the collection. 
• If the key exists, its value is updated with the new value. 
• Some important characteristics of a HashMap are its capacity, its load factor and the threshold resizing.