HashMap Java

In Java, a HashMap is a part of the Java Collections Framework and is used to store key-value pairs. It is an implementation of the Map interface, and it does not allow duplicate keys. Each key in a HashMap must be unique.

Here are some key features and characteristics of a HashMap in Java:

Key-Value Pairs:

A HashMap stores data in key-value pairs.Each key is associated with exactly one value.

Null Values:

Both keys and values in a HashMap can be null.

Ordering:

The order of elements in a HashMap is not guaranteed. If you need to maintain the order, you can use a LinkedHashMap.

Performance:

The HashMap class provides constant-time performance for basic operations (get and put) in the average case, assuming the hash function disperses elements properly.

Hashing:

HashMap uses a hash function to compute an index into the underlying array where the value is stored.The default hash function is based on the hashCode() method of the keys.

Collision Handling:

In case of hash collisions (two keys having the same hash code), HashMap uses a linked list to store multiple entries at the same index. If the linked list becomes too long, it gets transformed into a balanced tree for improved performance.

Capacity and Load Factor:

HashMap has an initial capacity and a load factor that determines when to resize the underlying array.The load factor is a measure of how full the HashMap is allowed to get before its capacity is automatically increased.

Methods:

Some commonly used methods include put(key, value), get(key), remove(key), containsKey(key), size(), and others.