Difference between HashMap and HashSet in Java.

HashMap and HashSet both are one of the most important classes of Java Collection framework.

Following are the important differences between HashMap and HashSet.

Example of Hashmap vs Hashset

JavaTester.java

 Live Demo

import java.util.HashSet;
public class JavaTester {
   public static void main(String[] args){
      HashSet<String> hs = new HashSet<String>();
      hs.add("John");
      hs.add("Smith");
      hs.add("Peter");
      System.out.println("Before adding duplicate values 

" + hs);
      hs.add("John");
      hs.add("Smith");
      System.out.println("
After adding duplicate values 

" + hs);
      hs.add(null);
      hs.add(null);
      System.out.println("
After adding null values 

" + hs);
   }
}

Output

Before adding duplicate values
[John, Smith, Peter]
After adding duplicate values
[John, Smith, Peter]
After adding null values
[null, John, Smith, Peter]

Example

JavaTester.java

 Live Demo

import java.util.HashMap;
public class JavaTester {
   public static void main(String[] args){
      HashMap<Integer, String> hm = new HashMap<Integer, String>();
      hm.put(12, "John");
      hm.put(2, "Smith");
      hm.put(7, "Peter");
      System.out.println("
HashMap object output :

" + hm);
      hm.put(12, "Smith");
      System.out.println("
After inserting duplicate key :

" + hm);
   }
}

Output

HashMap object output :
{2=Smith, 7=Peter, 12=John}
After inserting duplicate key :
{2=Smith, 7=Peter, 12=John}