Java HashSet

In this tutorial, we will learn about the Java HashSet class. We will learn about different hash set methods and operations with the help of examples.

The HashSet class of the Java Collections framework provides the functionalities of the hash table data structure.

Hashset class which is implemented in the collection framework is an inherent implementation of the hash table datastructure. The objects that we insert into the hashset does not guarantee to be inserted in the same order. The objects are inserted based on their hashcode. This class also allows the insertion of NULL elements. Let’s see how to create a set object using this class.

Example:

// Java program to demonstrate the 
// creation of Set object using 
// the Hashset class 
import java.util.*; 

class Codmistic
{ 
	public static void main(String[] args) 
	{ 
		Set<String> h = new HashSet<String>(); 

		// Adding elements into the HashSet 
		// using add() 
		h.add("India"); 
		h.add("Australia"); 
		h.add("South Africa"); 

		// Adding the duplicate 
		// element 
		h.add("India"); 

		// Displaying the HashSet 
		System.out.println(h); 

		// Removing items from HashSet 
		// using remove() 
		h.remove("Australia"); 
		System.out.println("Set after removing "
						+ "Australia:" + h); 

		// Iterating over hash set items 
		System.out.println("Iterating over set:"); 
		Iterator<String> i = h.iterator(); 
		while (i.hasNext()) 
			System.out.println(i.next()); 
	} 
} 

output:
[South Africa, Australia, India]
Set after removing Australia:[South Africa, India]
Iterating over set:
South Africa
India

Few important features of HashSet are:

• Implements Set Interface.
• Underlying data structure for HashSet is hashtable.
• As it implements the Set Interface, duplicate values are not allowed.
• Objects that you insert in HashSet are not guaranteed to be inserted in same order. Objects are inserted based on their hash code.
• NULL elements are allowed in HashSet.
• HashSet also implements Searlizable and Cloneable interfaces.

Methods in Java HashSet