Difference Between HashMap and TreeMap in Java

In this post, we will understand the difference between hashmap and treemap, associated with Java.

HashMap

It is a hash table in Java.
It is based on the implementation of ‘map’ interface.
It implements ‘Map, ‘Cloneable’, and ‘Serializable’ interfaces.
It allows a single null key.
It also allows multiple null values.
It is quicker in comparison to Treemap.
This is because it provides constant-time performances, i.e O(1) for operations like ‘get’ and ‘put’.
It doesn’t perform sorting on keys.
Hence it allows heterogeneous elements in the HashMap.
It doesn’t maintain the order of elements.
It can be used when a key-value pair in a sorted order is NOT needed.
It uses the ‘equals’ method of Object class to compare keys.
The ‘equals’ method of Map class overrides it.
It only contains basic methods like ‘KeySet’, ‘get’, ‘put’.

It is a tree structure used in Java.
It is based on the implementation of ‘map’ interface.
It implements ‘NavigableMap’, ‘Cloneable’, and the ‘Serializable’ interface.
It doesn’t allow null keys.
It allows multiple null values.
It allows homogeneous values as a key since it is sorted.
It is slow in comparison to HashMap since it provides complexity of O(log(n)) for most of the operations such as add(), remove() and contains().
It uses a Red-Black tree internally.
Red black tree is a self-balancing Binary Search Tree.
The compareTo() method is used in order to compare keys.
It has many functionalities such as tailMap(), firstKey(), lastKey(), pollFirstEntry(), pollLastEntry().
The elements are sorted in ascending order, also known as natural order.
It is used when the requirement is a key-value pair in a sorted order.

Published on 24-Mar-2021 12:32:51