difference between hashset and hashmap

by March 19, 2021 Java

Let’s learn difference between hashset and hashmap in java.

difference between hashset and hashmap

HashSetHashMap
We can store objects in HashSet. For example HashSet:{“Hello”, “World”}In HashMap we can store key and value pairs. For example {1 ->”Hello”, 2 ->”World”}
insertion order is not preserved. It is based on hashcode.does not maintain insertion order. It is based on Hash function.
has add() method.has put() method.
implements Set interface.implements Map interface.
do not allow duplicate elements.allows duplicate values. Does not allow duplicate keys.
allows single null value.allows single null key and any number of null values.

java hashmap example

import java.util.HashMap;
public class HashMapExample
{
   public static void main(String[] args)
   {
      HashMap<Integer, String> hm = new HashMap<Integer, String>();
      // add elements
      hm.put(10,"Apple");
      hm.put(20,"Banana");
      hm.put(30,"Cherry");
      hm.put(40,"Dragonfruit");
      // print HashMap elements
      System.out.println("HashMap elements: " + hm);
      // storing data with duplicate key
      hm.put(20, "Banana");
      System.out.println("After inserting duplicate key: " + hm);
   }
}

Output:

HashMap elements: {20=Banana, 40=Dragonfruit, 10=Apple, 30=Cherry}
After inserting duplicate key: {20=Banana, 40=Dragonfruit, 10=Apple, 30=Cherry}

java hashset example

import java.util.HashSet;
public class HashSetExample 
{
   public static void main(String[] args) 
   {
      HashSet<String> hs = new HashSet<String>(); 
      hs.add("Banana");    
      hs.add("Orange");    
      hs.add("Apple");   
      hs.add("Pineapple");  
      hs.add("Mango");
      System.out.println("Before adding duplicate values: " + hs);
      // adding duplicate elements 
      hs.add("Banana"); 
      hs.add("Orange");
      System.out.println("After adding duplicate values: " + hs);
      // adding null values
      hs.add(null); 
      hs.add(null);
      // printing HashSet elements 
      System.out.println("After adding null values: " + hs);
   }
}

Output:

Before adding duplicate values: [Apple, Mango, Pineapple, Orange, Banana]
After adding duplicate values: [Apple, Mango, Pineapple, Orange, Banana]
After adding null values: [null, Apple, Mango, Pineapple, Orange, Banana]

Also read – encapsulation in java