Map Interface in Java

In Java, the Map Interface is part of the java.util package and represents a collection of key-value pairs, where Keys should be unique, but values can be duplicated.

• It provides efficient retrieval, insertion, and deletion operations based on keys.
• HashMap and LinkedHashMap allow one null key, and TreeMap does NOT allow null keys (if natural ordering is used).
• Use ConcurrentHashMap for thread-safe operations, or Collections.synchronizedMap() to make an existing map synchronized.

Declaration of the Map interface

public interface Map<K, V>

• K -> Type of keys maintained by the map
• V -> Type of mapped values

Creating Map Objects

Since a Map is an interface, we cannot create its object directly. We must use a class that implements it (e.g., HashMap).

Map<String, Integer> hm = new HashMap<>();

import java.util.HashMap;
import java.util.Map;

public class Geeks{
    
    public static void main(String[] args){
        
        // Create a Map using HashMap
        Map<String, Integer> m = new HashMap<>();

        // Adding key-value pairs to the map
        m.put("Geek1", 1);
        m.put("Geek2", 2);
        m.put("Geek3", 3);

        System.out.println("Map elements: " + m);
    }
}

Map elements: {Geek3=3, Geek2=2, Geek1=1}

Hierarchy of Map

It is part of the Java Collections Framework, and its key implementation classes include HashMap, LinkedHashMap, TreeMap, and Hashtable.