Java HashMap class

Points to remember

Java HashMap class contains values based on the key.
Java HashMap class contains only unique keys.
Java HashMap class may have one null key and multiple null values.
Java HashMap class is non synchronized.
Java HashMap class maintains no order.
The initial default capacity of Java HashMap class is 16 with a load factor of 0.75.

import java.util.*;  
public class HashMap2 {  
   public static void main(String args[]) {  
    HashMap<Integer,String> map=new HashMap<Integer,String>();          
      map.put(100,"Amit");    
      map.put(101,"Vijay");    
      map.put(102,"Rahul");  
      map.put(103, "Gaurav");  
    System.out.println("Initial list of elements: "+map);  
    //key-based removal  
    map.remove(100);  
    System.out.println("Updated list of elements: "+map);  
    //value-based removal  
    map.remove(101);  
    System.out.println("Updated list of elements: "+map);  
    //key-value pair based removal  
    map.remove(102, "Rahul");  
    System.out.println("Updated list of elements: "+map);  
   }      
}

Output

Initial list of elements: {100=Amit, 101=Vijay, 102=Rahul, 103=Gaurav}
Updated list of elements: {101=Vijay, 102=Rahul, 103=Gaurav}
Updated list of elements: {102=Rahul, 103=Gaurav}
Updated list of elements: {103=Gaurav}