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Map - Java Example Program


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

class MapTest
{
    public static void main(String arg[])
    {
        Map<String, String> m = new HashMap<String, String>();
        Map<String, String> m1 = new HashMap<String, String>();
        System.out.println("Map objects equal : " + m.equals(m1)); // Equals method
        
        m.put("8", "Prakash"); // Put method
        m.put("31", "Shabaz");
        m.put("12", "Raj");
        m.put("14", "Praveen");
        m.put("5", "Gopi");
        
        System.out.println("Map Elements : " + m); // Display map elements
        System.out.println("Size of Map : " + m.size());
        System.out.println("Key contains : " + m.containsKey("31")); // LINE A
        System.out.println("Value contains : " + m.containsValue("Raj")); // LINE B
        System.out.println("Gets the value of key : " + m.get("14")); // LINE C
        System.out.println("Hash code for map : " + m.hashCode());
        System.out.println("Is map empty : " + m.isEmpty());
        System.out.println("Removes the key value : " + m.remove("12")); // LINE D
        System.out.println("Key set : " + m.keySet()); // LINE E
        System.out.println("Collection values : " + m.values()); // LINE F
        
        m1.putAll(m); // LINE G
        m.clear();
        System.out.println("Map after clear : " + m);
        System.out.println("All data of m is put into m1 map : " + m1);
        System.out.println("Entry set : " + m1.entrySet());    
    }
}
OUTPUT

Map objects equal : true
Map Elements : {5=Gopi, 31=Shabaz, 8=Prakash, 14=Praveen, 12=Raj}
Size of Map : 5
Key contains : true
Value contains : true
Gets the value of key : Praveen
Hash code for map : 867799845
Is map empty : false
Removes the key value : Raj
Key set : [5, 31, 8, 14]
Collection values : [Gopi, Shabaz, Prakash, Praveen]
Map after clear : {}
All data of m is put into m1 map : {5=Gopi, 31=Shabaz, 8=Prakash, 14=Praveen}
Entry set : [5=Gopi, 31=Shabaz, 8=Prakash, 14=Praveen]

DESCRIPTION

In this program, all the Map methods are applied on map object. The map is of type HashMap. It contains five elements.

THINGS TO TRY
  • At LINE A replace 31 by 5 to see that output is true. Which means key 5 is present in map. Enter any other key which is not in the map to return false. The same thing repeat for value at LINE B.
  • At LINE C give any key to return the value associated with that key. It returns null if the key does not exist in map.
  • at LINE D, remove is used to delete the element from map. Try with key 5.

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