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HashMap class

  • A HashMap contains values based on the key. It implements the Map interface and extends AbstractMap class.
  • It contains only unique elements.
  • It may have one null key and multiple null values.
  • It maintains no order.

Hierarchy of HashMap class:


Example of HashMap class:

  1. import java.util.*;
  2. class TestCollection13{
  3.  public static void main(String args[]){
  4.   HashMap<Integer,String> hm=new HashMap<Integer,String>();
  5.   hm.put(100,“Amit”);
  6.   hm.put(101,“Vijay”);
  7.   hm.put(102,“Rahul”);
  8.   for(Map.Entry m:hm.entrySet()){
  9.    System.out.println(m.getKey()+” “+m.getValue());
  10.   }
  11.  }
  12. }


Output:102 Rahul
       100 Amit
       101 Vijay

What is difference between HashSet and HashMap?

HashSet contains only values whereas HashMap contains entry(key and value).