HashMap In Java

In Java, HashMap is a part of the java. util package and is used to store key-value pairs. It is a part of the Java Collections Framework and implements the Map interface. Here are some key points about HashMap:

1. Key-Value Pairs:

   • Each entry in a HashMap is a key-value pair.

   • Keys and values can be of any non-null object type.

2. Null Values:

   • Both keys and values can be null.

   • However, there can be only one null key in a HashMap.

3. No Duplicate Keys:

   • Keys in a HashMap must be unique.

   • If you try to insert a key-value pair with an existing key, the new value will overwrite the existing value associated with that key.

4. Ordering:

   • The order of the key-value pairs in a HashMap is not guaranteed.

   • If you need ordering, you can use a LinkedHashMap, which maintains the order of insertion.

5. Performance:

   • HashMap provides constant-time performance for the basic operations (get and put) on average, assuming a good hash function and proper load factor.

   • The load factor is a measure of how full the HashMap is allowed to get before its capacity is automatically increased.

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