Java program to calculate the union of two sets

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In this example, we will learn to calculate the union of two sets in Java.

To understand this example, you should understand the followingJava ProgrammingTopic:

• Java Set Interface

• Java HashSet Class

Example1Using addAll() to calculate the union of two sets

import java.util.HashSet;
import java.util.Set;
class Main {
　　public static void main(String[] args) {
　　　　//Create the first collection
　　　　Set<Integer> evenNumbers = new HashSet<>();
　　　　evenNumbers.add(2);
　　　　evenNumbers.add(4);
　　　　System.out.println("Set1: "　+　evenNumbers);
　　　　//Create the second collection
　　　　Set<Integer> numbers = new HashSet<>();
　　　　numbers.add(1);
　　　　numbers.add(3);
　　　　System.out.println("Set2: "　+　numbers);
　　　　//The union of the two sets
　　　　numbers.addAll(evenNumbers);
　　　　System.out.println("The union of the two sets: "　+　numbers);
　　}
}

Output Result

Set1: [2,　4]
Set2: [1,　3]
The union of the two sets: [1,　2,　3,　4]

In the above example, we created two collections named evenNumbers and numbers. We implemented the collection using the HashSet class. Note this line,

numbers.addAll(evenNumbers);

In this example, we use the addAll() method to obtain the union of two sets.

Example2Using Guava library to get the union of two sets

import java.util.HashSet;
import java.util.Set;
import com.google.common.collect.Sets;
class Main {
　　public static void main(String[] args) {
　　　　//Create the first collection
　　　　Set<String> languages1　= new HashSet<>();
　　　　languages1.add("Java");
　　　　languages1.add("Python");
　　　　System.out.println("Programming languages: "　+　languages1);
　　　　//Create the second collection
　　　　Set<String> languages2　= new HashSet<>();
　　　　languages2.add("English");
　　　　languages2.add("Spanish");
　　　　System.out.println("Human Languages: ",　+　languages2);
　　　　Set<String> unionSet = Sets.union(languages1, languages2);
　　　　System.out.println("The union is: ",　+　unionSet);
　　}
}

Output Result

Programming Languages: [Java, Python]
Human Languages: [English, Spanish]
The union is: [Java, Python, English, Spanish]

In the above example, we useGuava LibraryTo run this program, you need to implement it by adding the Guava library to the dependencies.

Here, we use the union() method of the Sets class that exists in the Guava library.

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