Sort a List in Ascending and Descending Order Using the Java 8 Stream API

        In one of my previous posts, I covered several Java 8 Stream API coding questions and answers. In this post, we will discuss one of the most commonly asked coding interview questions: how to sort a list in ascending and descending order using the Java 8 Stream API.

1) Sort a List of Strings in Ascending Order Using the Java 8 Stream API

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

public class SortExample {

    public static void main(String[] args) {

	 List<String> listOfStrings = Arrays.asList("A", "E", "B", "C");

         listOfStrings.stream().sorted().forEach(s -> System.out.println(s));
    }

}

Output:- A

              B

              C

              E

2) Sort a List of Strings in Descending Order Using the Java 8 Stream API

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

public class SortExample {

     public static void main(String[] args) {

	  List<String> listOfStrings = Arrays.asList("A", "E", "B", "C");

          listOfStrings.stream().sorted(Comparator.reverseOrder())

                                              .forEach(s -> System.out.println(s));
     }

}

Output:-   E

                C

                B

                A

3) Sort a List of Custom Java Objects (Employee Class) in Ascending or Descending Order Using the Java 8 Stream API

Employee.java,

public class Employee {
	
	private Long id;
	private String firstName;
	private String lastName;
	private String address;
      
        //constructor, setter and getter
       // and toString metghod
}

SortExample.java,

package com.main;

import java.util.ArrayList;
import java.util.List;

public class SortExample {

     public static void main(String[] args) {
		
	 Employee e1 = new Employee(1L, "Anil", "Nivargi", "XYZ");
	 Employee e2 = new Employee(2L, "Mahesh", "Nivargi", "XYZ");

	 List<Employee> employeeList = new ArrayList<>();
	 employeeList.add(e1);
	 employeeList.add(e2);
		
	  System.out.println("Sort a list in ascending order using firstName -");
		
	  //sort a list in ascending order using firstName
	  employeeList.stream().sorted((s1,s2) -> 

                        s1.getFirstName().compareTo(s2.getFirstName())).forEach(

                                 s -> System.out.println(s));

		
	  System.out.println("Sort a list in descending order using firstName -");
		
	    //sort a list in descending order using firstName
	  employeeList.stream().sorted((s1,s2) -> 

                        s2.getFirstName().compareTo(s1.getFirstName())).forEach(

                                 s -> System.out.println(s));

     }

}

Output:- 

Sort a list in ascending order using firstName -
Employee [id=1, firstName=Anil, lastName=Nivargi, address=XYZ]
Employee [id=2, firstName=Mahesh, lastName=Nivargi, address=XYZ]
Sort a list in descending order using firstName -
Employee [id=2, firstName=Mahesh, lastName=Nivargi, address=XYZ]
Employee [id=1, firstName=Anil, lastName=Nivargi, address=XYZ]

Thank you reading the blog post.

Reference Posts:-

1) Java 8 stream coding questions

2) Difference between map and flatMap method in java 8

3) Find duplicate element from the list using stream

4) Java 8 Optional class usages