Compare Two Sets in Java

In Java, Set is a collection interface used to store unique elements. Set doesn't allow users to enter duplicate values in it. We often need to compare two sets to check whether they contain the same elements or not, and both sets should also have the same size.

The Set interface provides the equals() method for verifying the equality of the given two sets. It returns either true or false based on the equality of both sets. If both the sets contain the same elements and have the same size, the method returns true.

The equals() method has the following syntax:

Let's take some examples to understand how we can use the equals() method to compare two sets.

CompareSetExample1.java

import java.util.*
// create CompareSetExample1 class to compare two sets
public class CompareSetExample1 {
	// main() method start
	public static void main(String[] argv)
	{
		// create an object of the HashSet class
		Set<String> set1 = new HashSet<String>();
		// fill values in the set1
		set1.add("Paul");
		set1.add("Donal");
		set1.add("William");
		set1.add("Johnson");
		set1.add("Emma");
		// print the values and size of the set1
		System.out.println("The values in the 1st set are: "+ set1);
		System.out.println();
		System.out.println("The size of the 1st set is: "+ set1.size());
		// create another object of the Hashset class
		Set<String> set2 = new HashSet<String>();
		// fill values in the set2
		set2.add("Paul");
		set2.add("Johnson");
		set2.add("Donal");
		set2.add("Emma");
		set2.add("William");
		// print the values and size of the set2
		System.out.println("The values in the 2nd set are: "+ set2);
		System.out.println();
		System.out.println("The size of the 2nd set is: "+ set2.size());
		// use equals() method to compare set1 and set2
		boolean result = set1.equals(set2);
		// print the result
		if(result) {
			System.out.println("Set1 and Set2 are equal.");
		}else {
			System.out.println("Set1 and Set2 are not equal.");
		}
	}
}

Output:

CompareSetExample2.java

import java.util.*;
// create CompareSetExample2 class to compare two sets
public class CompareSetExample2 {
	// main() method start
	public static void main(String[] argv)
	{
		// create an object of the HashSet class
		Set<Integer> oldAges = new HashSet<Integer>();
		// fill values in the set1
		oldAges.add(5);
		oldAges.add(7);
		oldAges.add(9);
		oldAges.add(11);
		oldAges.add(13);
		oldAges.add(11);
		// print the values and size of the set1
		System.out.println("The values in the 1st set are: "+ oldAges);
		System.out.println("The size of the 1st set is: "+ oldAges.size());
		System.out.println();
		// create another object of the Hashset class
		Set<Integer> newAges = new HashSet<Integer>();
		// fill values in the set2
		newAges.add(5);
		newAges.add(7);
		newAges.add(9);
		newAges.add(11);
		newAges.add(13);
		// print the values and size of the set2
		System.out.println("The values in the 2nd set are: "+ newAges);
		System.out.println("The size of the 2nd set is: "+ newAges.size());
		System.out.println();
		// use equals() method to compare set1 and set2
		boolean result = oldAges.equals(newAges);
		// print the result
		if(result) {
			System.out.println("Set1 and Set2 are equal.");
		}else {
			System.out.println("Set1 and Set2 are not equal.");
		}
	}
}

Output:

So, the equals() method is one of the most used and fast ways to compare two sets in Java. The equals() method compares two sets based on the type of the elements, size of the set, and value of the elements.

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