Java program calculates the intersection of two collections

Comprehensive Java Examples

In this example, we will learn to calculate the intersection of two collections in Java.

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

• Java Set Interface

• Java HashSet Class

Example1Calculate the intersection of two collections

import java.util.HashSet;
import java.util.Set;
class Main {
　　public static void main(String[] args) {
　　　　//Create the first collection
　　　　Set<Integer> primeNumbers = new HashSet<>();
　　　　primeNumbers.add(2);
　　　　primeNumbers.add(3);
　　　　System.out.println("Prime numbers: ",　+　primeNumbers);
　　　　//Create the second collection
　　　　Set<Integer> evenNumbers = new HashSet<>();
　　　　evenNumbers.add(2);
　　　　evenNumbers.add(4);
　　　　System.out.println("Even numbers: ",　+　evenNumbers);
　　　　//Intersection of two collections
　　　　evenNumbers.retainAll(primeNumbers);
　　　　System.out.println("Intersection of two collections: ",　+　evenNumbers);
　　}
}

Output Result

Prime numbers: [2,　3]
Even numbers: [2,　4]
Intersection of two collections: [2]

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

evenNumbers.retainAll(primeNumbers);

In this example, we use the retainAll() method to obtain the intersection of two collections.

Example2Use Guava library to get the union of two collections

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> backend = new HashSet<>();
　　　　backend.add("Java");
　　　　backend.add("JavaScript");
　　　　System.out.println("Backend language: ",　+　backend);
　　　　//Create the second collection
　　　　Set<String> frontend = new HashSet<>();
　　　　frontend.add("JavaScript");
　　　　frontend.add("CSS");
　　　　System.out.println("Front-end Language: ",　+　frontend);
　　　　Set<String> intersect = Sets.intersection(backend, frontend);
　　　　System.out.println("General Language: ",　+　intersect);
　　}
}

Output Result

Back-end Language: [Java, JavaScript]
Front-end Language: [JavaScript, CSS]
General Language: [JavaScript]

In the above example, we use the Guava library to get the intersection of two collections. To run this program, you need to implement it by adding the Guava library to the dependencies.

Here, we use the intersection() method of the Sets class from the Guava library.

Comprehensive Java Examples