HashMap Implementation

When we create a HashMap, it is stored in JVM heap memory.

When initialisation, it is created 16 buckets hashMap.

According to the above output, 1st bucket’s hashing has been changed because the hash map capacity has been exceeded more than load factor percentage and rehashing came to the picture.

Here you can see, in hashmap implementation, we are using Linked list implementation according to the above picture.

IMPORTANT- Here we are using Object hashCode() and equals() method for the HashMap implementation. These methods not for primitives types. That is why HashMap is not supported for primitives types. It is supported only objects.

Hash maps store both key and value in the bucket location as a Map.Entry object. Please check below screen shot.

a) if it is using LinkedList, time complexity is O(n) because each of the keys in the linked list should be compared with the provided key object using equals methods.

b) If it is using Tree, time complexity is O(log(n)).

When we need to get a value of linked list, we should traverse one by one from the beginning.

Example 1

Output —

Example 2

Put same key into HashMap.

Output —

Value of Pramod override with new value.

Example 3 -

Put null values into hashmap

Output-

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