Java Lambda Expression Comparator Example

In this post, we will see how to use Lambda expression to implement the Comparator interface with an example.

Java Lambda Expression Example: Comparator

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class JLEComparatorExample {

    public static void main(String[] args) {

        List<Person> listOfPerson = new ArrayList<Person>();
        listOfPerson.add(new Person("abc", 27));
        listOfPerson.add(new Person("mno", 26));
        listOfPerson.add(new Person("pqr", 28));
        listOfPerson.add(new Person("xyz", 27));

        // Without lambda expression.
        // Sort list by age
        Comparator<Person> comparator = new Comparator<Person>() {
            @Override
            public int compare(Person o1, Person o2) {
                return o1.getAge() - o2.getAge();
            }
        };

        Collections.sort(listOfPerson, comparator);

        System.out.println(" sort persons by age in ascending order");
        for (Person person : listOfPerson) {
            System.out.println(" Person name : " + person.getName());
        }

        // Witht lambda expression.
        // Sort list by age

        Collections.sort(listOfPerson, (Person o1, Person o2) -> {
            return o1.getAge() - o2.getAge();
        });
        // Use forEach method added in java 8
        System.out.println(" sort persons by age in ascending order");
        listOfPerson.forEach(
           (person) -> System.out.println(" Person name : " + person.getName()));
        }
  }

class Person {
    private String name;
    private int age;

    public Person(String name, int age) {
       super();
       this.name = name;
       this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

References

• https://www.javaguides.net/2020/03/java-lambda-expressions-examples.html
• https://www.javaguides.net/2018/07/java-8-lambda-expressions.html