Java 8 Stream - Sorting with Comparator Example

In this tutorial, we will see how to sort List (ArrayList) in ascending and descending order using Java 8 Stream APIs.

Learn Stream API at https://www.javaguides.net/p/java-8-stream-api-tutorial.html.

Table of contents

1. Sort List of String objects in Ascending order using Java 8 Stream APIs
2. Sort List of String objects in Descending order using Java 8 Stream APIs
3. Sort List of Employee objects in Ascending order using Java 8 Stream APIs
4. Sort List of Employee objects in Descending order using Java 8 Stream APIs

1. Sort List of String objects in Ascending order using Java 8 Stream APIs

This example demonstrates different ways to sort List of String objects in Ascending order using Java 8 Stream APIs:

import java.util.ArrayList;

import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;

public class StreamListSorting {
    public static void main(String[] args) {

        List < String > fruits = new ArrayList < String > ();
        fruits.add("Banana");
        fruits.add("Apple");
        fruits.add("Mango");
        fruits.add("Orange");

        List < String > sortedList = fruits.stream().sorted(Comparator.naturalOrder()).collect(Collectors.toList());
        System.out.println(sortedList);

        List < String > sortedList1 = fruits.stream().sorted((o1, o2) -> o1.compareTo(o2)).collect(Collectors.toList());
        System.out.println(sortedList1);

        List < String > sortedList2 = fruits.stream().sorted().collect(Collectors.toList());
        System.out.println(sortedList2);
    }
}

Output:

[Apple, Banana, Mango, Orange]
[Apple, Banana, Mango, Orange]
[Apple, Banana, Mango, Orange]

2. Sort List of String objects in Descending order using Java 8 Stream APIs

This example demonstrates different ways to sort List of String objects in descending order using Java 8 Stream APIs:

import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;

public class StreamListSorting {
    public static void main(String[] args) {

        List < String > fruits = new ArrayList < String > ();
        fruits.add("Banana");
        fruits.add("Apple");
        fruits.add("Mango");
        fruits.add("Orange");

        // descending order
        List < String > sortedList3 = fruits.stream().sorted(Comparator.reverseOrder()).collect(Collectors.toList());
        System.out.println(sortedList3);

        List < String > sortedList4 = fruits.stream().sorted((o1, o2) -> o2.compareTo(o1)).collect(Collectors.toList());
        System.out.println(sortedList4);
    }
}

Output:

[Orange, Mango, Banana, Apple]
[Orange, Mango, Banana, Apple]

3. Sort List of Employee objects in Ascending order using Java 8 Stream APIs

Let's first create an Employee model class:

package com.java.tutorials.sorting;

public class Employee {
    private int id;
    private String name;
    private int age;
    private long salary;
    public Employee(int id, String name, int age, long salary) {
        super();
        this.id = id;
        this.name = name;
        this.age = age;
        this.salary = salary;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    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;
    }
    public long getSalary() {
        return salary;
    }
    public void setSalary(long salary) {
        this.salary = salary;
    }
    @Override
    public String toString() {
        return "Employee [id=" + id + ", name=" + name + ", age=" + age + ", salary=" + salary + "]";
    }
}

This example demonstrates how to sort an Employee by salary in ascending order using Java 8 Stream APIs:

import java.util.ArrayList;

import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;

public class StreamListSorting {
    public static void main(String[] args) {

        // sort employee by salary in ascending order
        List < Employee > employees = new ArrayList < Employee > ();
        employees.add(new Employee(10, "Ramesh", 30, 400000));
        employees.add(new Employee(20, "John", 29, 350000));
        employees.add(new Employee(30, "Tom", 30, 450000));
        employees.add(new Employee(40, "Pramod", 29, 500000));

        List < Employee > employeesSortedList1 = employees.stream()
            .sorted((o1, o2) -> (int)(o1.getSalary() - o2.getSalary())).collect(Collectors.toList());
        System.out.println(employeesSortedList1);

        List < Employee > employeesSortedList2 = employees.stream()
            .sorted(Comparator.comparingLong(Employee::getSalary)).collect(Collectors.toList()); //ascending order
        System.out.println(employeesSortedList2);
    }
}

Output:

[Employee [id=20, name=John, age=29, salary=350000], Employee [id=10, name=Ramesh, age=30, salary=400000], Employee [id=30, name=Tom, age=30, salary=450000], Employee [id=40, name=Pramod, age=29, salary=500000]]
[Employee [id=20, name=John, age=29, salary=350000], Employee [id=10, name=Ramesh, age=30, salary=400000], Employee [id=30, name=Tom, age=30, salary=450000], Employee [id=40, name=Pramod, age=29, salary=500000]]

4. Sort List of Employee objects in Descending order using Java 8 Stream APIs

This example demonstrates how to sort an Employee by salary in descending order using Java 8 Stream APIs:

import java.util.ArrayList;

import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;

public class StreamListSorting {
    public static void main(String[] args) {

        // sort employee by salary in ascending order
        List < Employee > employees = new ArrayList < Employee > ();
        employees.add(new Employee(10, "Ramesh", 30, 400000));
        employees.add(new Employee(20, "John", 29, 350000));
        employees.add(new Employee(30, "Tom", 30, 450000));
        employees.add(new Employee(40, "Pramod", 29, 500000));

        List < Employee > employeesSortedList1 = employees.stream()
            .sorted((o1, o2) -> (int)(o2.getSalary() - o1.getSalary())).collect(Collectors.toList());
        System.out.println(employeesSortedList1);

        List < Employee > employeesSortedList2 = employees.stream()
            .sorted(Comparator.comparingLong(Employee::getSalary).reversed()).collect(Collectors.toList()); //ascending order
        System.out.println(employeesSortedList2);
    }
}

Output:

[Employee [id=40, name=Pramod, age=29, salary=500000], Employee [id=30, name=Tom, age=30, salary=450000], Employee [id=10, name=Ramesh, age=30, salary=400000], Employee [id=20, name=John, age=29, salary=350000]]
[Employee [id=40, name=Pramod, age=29, salary=500000], Employee [id=30, name=Tom, age=30, salary=450000], Employee [id=10, name=Ramesh, age=30, salary=400000], Employee [id=20, name=John, age=29, salary=350000]]

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