Java HashSet clear() Method

The HashSet.clear() method in Java is used to remove all elements from a HashSet. This guide will cover the method’s usage, explain how it works, and provide examples to demonstrate its functionality.

Table of Contents

1. Introduction
2. clear Method Syntax
3. Examples
   • Clearing a HashSet
   • Checking If a HashSet Is Empty After Clearing
4. Conclusion

Introduction

The HashSet.clear() method is a member of the HashSet class in Java. It allows you to remove all elements from a HashSet, effectively making it empty. This method is useful when you want to reuse an existing HashSet without creating a new instance.

clear Method Syntax

The syntax for the clear method is as follows:

public void clear()

• The method does not take any parameters.
• The method does not return any value.

Examples

Clearing a HashSet

The clear method can be used to remove all elements from a HashSet.

Example

import java.util.HashSet;

public class ClearExample {
    public static void main(String[] args) {
        // Creating a HashSet of Strings
        HashSet<String> languages = new HashSet<>();

        // Adding elements to the HashSet
        languages.add("Java");
        languages.add("Python");
        languages.add("C");

        // Printing the HashSet before clearing
        System.out.println("HashSet before clear: " + languages);

        // Clearing the HashSet
        languages.clear();

        // Printing the HashSet after clearing
        System.out.println("HashSet after clear: " + languages);
    }
}

Output:

HashSet before clear: [Java, C, Python]
HashSet after clear: []

Checking If a HashSet Is Empty After Clearing

After clearing a HashSet, you can check if it is empty using the isEmpty method.

Example

import java.util.HashSet;

public class ClearAndCheckExample {
    public static void main(String[] args) {
        // Creating a HashSet of Strings
        HashSet<String> languages = new HashSet<>();

        // Adding elements to the HashSet
        languages.add("Java");
        languages.add("Python");
        languages.add("C");

        // Clearing the HashSet
        languages.clear();

        // Checking if the HashSet is empty
        boolean isEmpty = languages.isEmpty();

        // Printing the result
        System.out.println("Is HashSet empty after clear? " + isEmpty);
    }
}

Output:

Is HashSet empty after clear? true

Conclusion

The HashSet.clear() method in Java provides a way to remove all elements from a HashSet, making it empty. This can be useful for reusing a HashSet without creating a new instance. After calling the clear method, the HashSet will be empty, and you can verify this using the isEmpty method.