HashMap In Java

In Java, HashMap is a part of the Java Collections Framework and is used to store key-value pairs. It is implemented as a hash table, providing constant-time performance for basic operations (like get and put) in the average case.

Here are some key points about HashMap in Java:

Key-Value Pairs:

Each element in a HashMap is a key-value pair.
Keys must be unique within a HashMap.
Values can be duplicated.
Null Keys and Values:

HashMap allows one null key and multiple null values.
Performance:

HashMap provides constant-time performance for the basic operations (get and put) on average.
However, the actual performance may degrade in case of hash collisions.
Ordering:

The order of elements in a HashMap is not guaranteed. If you need a specific order, consider using LinkedHashMap.
Methods:

put(K key, V value): Adds a key-value pair to the map.
get(Object key): Retrieves the value associated with the specified key.
remove(Object key): Removes the key-value pair associated with the specified key.
containsKey(Object key): Returns true if the map contains the specified key.
containsValue(Object value): Returns true if the map contains the specified value.