Java HashMap

The Hash Map uses <Key, value> pair to store data. The Key is unique for each data in a map. There can be one NULL key in a map.

Class Name:  HashMapExample.java

import java.util.*;

public class HashMapExample1 {

       public static void main(String[] args) {

              Map<String,Integer> map1 = new HashMap<String,Integer>();

      

              //Map to store name and age Map<Key,Value>

              map1.put("SAM", 18);

              map1.put("DONALD", 26);

              map1.put("BILLY", 24);

              map1.put("TRINITY", 18);

              map1.put("JIM", null);

              map1.put(null, 24);

              System.out.println("Contents of Map : "+map1);

             

              //KeySet() returns all key in the Map

              System.out.println("Keyset : "+map1.keySet());

             

              //Remove a value from map

              map1.remove("JIM");

              System.out.println("Contents of Map after removing : "+map1);

             

              //Getting particular value using key

              System.out.println("Value of map at given KEY : "+map1.get("SAM"));

             

              //Size of map

              System.out.println("Size of the give map : "+map1.size());

             

              //Getting all values in the map

              System.out.println("Values in map : "+map1.values());

             

              //To check if the map is empty - returns true if map is empty

              System.out.println("Is the map empty : "+map1.isEmpty());

       }

}

OUTPUT:

Contents of Map : {null=24, DONALD=26, SAM=18, TRINITY=18, JIM=null, BILLY=24}

Keyset : [null, DONALD, SAM, TRINITY, JIM, BILLY]

Contents of Map after removing : {null=24, DONALD=26, SAM=18, TRINITY=18, BILLY=24}

Value of map at given KEY : 18

Size of the givem map : 5

Values in map : [24, 26, 18, 18, 24]

Is the map empty : false