Hashset Example in Java

Introduction

HashSet is a classic Java console program that demonstrates the concept with complete source code and sample output. The Collections Framework provides ArrayList, HashMap, HashSet and related data structures.

This tutorial walks through the program line by line, explains how the logic works, and highlights best practices you can apply in your own code.

Definition

A set can’t have any duplicate elements in it. Additionally, the set has no set order. As such, elements can’t be found by index. HashSet uses a hash table.

Syntax

HashSet  Variable_name = new HashSet();

HashSet Example Program

import java.util.*;

class HashSetExample{
	public static void main(String[] args){
		HashSet hs=new HashSet();
		hs.add("d");
		hs.add("c");
		hs.add("b");
		hs.add("a");
		hs.add("c");
		System.out.println("Hashset is "+hs);
		System.out.println("Size of Hashset is "+hs.size());
	}
}

Sample Output

Hashset is [d, b, c, a]
Size of Hashset is 4

When to use

Use this hashset example when learning or revising core Java syntax.

How it works

1. Execution begins in the main method — the JVM calls this method when you run the class.

2. import java.util.*; imports a class used later in the program.

3. HashSet hs=new HashSet(); updates a variable used in the calculation or output.

4. A println / print call writes text to the console — part of the sample output below.

5. A println / print call writes text to the console — part of the sample output below.

6. Compare your console output with the sample output for HashSet to confirm the program behaves correctly.

Best Practices

• Use meaningful variable and class names that describe their purpose.
• Compile and run the program locally — modify values to see how output changes.
• Read compiler errors carefully; they usually point to the exact line to fix.

Common Mistakes

• Copying code without understanding each line — practice by changing one statement at a time.
• Mismatching the public class name and the .java filename.
• Forgetting semicolons at the end of statements.