In this tutorials, we are going to see how to sort user defined objects using Java 8 comparator with lambda expression. In the previous tutorials we have discussed about what is comparator in Java,  you can seen the basic functionality of the comparator in java here.

Java 8 Comparator :

Sorting the Cricketer objects with  comparator with Java 8 extreme feature Lambda expressions.

Create a Cricketer Pojo class.

Cricketer.java

class Cricketer {
    private int id;
    private String name;
    private int score;

    public Cricketer(int id, String name, int score) {
        super();
        this.id = id;
        this.name = name;
        this.score = score;
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public int getScore() {
        return score;
    }

    @Override
    public String toString() {
        return "Student [id=" + id + ", name=" + name + ", score=" + score
                + "]";
    }

}

Comparator with Lambda :

package com.onlinetutorialspoint.java8;

import java.util.Arrays;
import java.util.List;

public class Java8_Comparator_with_Lambda {
    public static void main(String[] args) {
        List<Cricketer> cricketer = Arrays.asList(
                new Cricketer(1, "Dhoni", 102), new Cricketer(2, "Virat Kohli",
                        98), new Cricketer(3, "Rohit Sharma", 75),
                new Cricketer(4, "Youraj Singh", 84), new Cricketer(5, "Raina",
                        98));

        System.out.println("Before Sorting..");
        cricketer.forEach(System.out::println);

        sortByName(cricketer);

    }

    public static void sortByScore(List<Cricketer> crickters) {
        crickters.sort((Cricketer o1, Cricketer o2) -> o1.getScore()
                - o2.getScore());
        System.out.println("After Sorting..");
        crickters.forEach((developer) -> System.out.println(developer));
    }

    public static void sortByName(List<Cricketer> crickters) {
        crickters.sort((Cricketer c1, Cricketer c2) -> c1.getName().compareTo(
                c2.getName()));
        System.out.println("After Sorting..");
        crickters.forEach((developer) -> System.out.println(developer));
    }
}

Output:

Before Sorting..
Student [id=1, name=Dhoni, score=102]
Student [id=2, name=Virat Kohli, score=98]
Student [id=3, name=Rohit Sharma, score=75]
Student [id=4, name=Youraj Singh, score=84]
Student [id=5, name=Raina, score=98]
After Sorting..
Student [id=1, name=Dhoni, score=102]
Student [id=5, name=Raina, score=98]
Student [id=3, name=Rohit Sharma, score=75]
Student [id=2, name=Virat Kohli, score=98]
Student [id=4, name=Youraj Singh, score=84]

Comparing with  Stream :

package com.onlinetutorialspoint.java8;

import java.util.Arrays;
import java.util.Comparator;
import static java.util.Comparator.*;
import java.util.List;


public class Java8_Comparator_with_Lambda {
    public static void main(String[] args) {
        List<Cricketer> cricketer = Arrays.asList(
                new Cricketer(1, "Dhoni", 102), new Cricketer(2, "Virat Kohli",
                        98), new Cricketer(3, "Rohit Sharma", 75),
                new Cricketer(4, "Youraj Singh", 84), new Cricketer(5, "Raina",
                        98));
        
        sortUsingStream(cricketer, comparing(Cricketer::getName));

    }
   
    public static void sortUsingStream(List<Cricketer> crickters,Comparator<Cricketer> comp){
        crickters.stream().sorted(comp).forEach(System.out::println);
    }
}

Here comparing() is a static method from java.util.Comparator, it accepts a function that extracts a java.lang.Comparable sort key from a type {T}, and returns a  Comparator<T> that compares by that sort key.
Output:

Student [id=1, name=Dhoni, score=102]
Student [id=5, name=Raina, score=98]
Student [id=3, name=Rohit Sharma, score=75]
Student [id=2, name=Virat Kohli, score=98]
Student [id=4, name=Youraj Singh, score=84]

Happy Learning:)