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Hey guys in this post let’s discuss aboutsorted()introduced in Java 8 java.util.stream.Steam interface. On the streams() we can perform some aggregate operations such as filter(), sorted() and map(). In this post let’s discuss about sorted().

Let’s look at the first example on how to sort the array of strings in ascending and descending order.

Example1.java

import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;

public class Test {
	public static void main(String[] args) throws IOException {
		
		List<String> fruits = Arrays.asList("Mango", "Apple", "Orange", "Grapes", "Pineapple", "Banana");
		List<String> sortedList = new ArrayList<String>();
		//sort in ascending order
		sortedList = fruits.stream().sorted(Comparator.naturalOrder()).collect(Collectors.toList());
		sortedList.forEach(System.out::println);
		System.out.println("********************************");
		//sort in descending order
		sortedList = fruits.stream().sorted(Comparator.reverseOrder()).collect(Collectors.toList());
		sortedList.forEach(System.out::println);
	}
}

We can use Comparator provided methods to sort the items, naturalOrder() will sort in ascending order and reverseOrder(), will sort in desceding order.

Person.java

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

Example2.java

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

public class Test {
	public static void main(String[] args) {
		
		List<Person> list = Arrays.asList(
			new Person(1, "Ramesh", 45, 35000),
			new Person(2, "Bushan", 29, 22000),
			new Person(3, "Shankar", 33, 29000),
			new Person(4, "Chaitra", 32, 50000)
		);
		list.stream().sorted(Comparator.comparingInt(Person::getAge)).forEach(System.out::println);
		System.out.println("****************************");
		list.stream().sorted(Comparator.comparingInt(Person::getAge).reversed()).forEach(System.out::println);
	}
}

To sort the integer values, Comparator provides comparingInt(), using which we can sort the items. reversed() will sort the items in descending order.




Example3.java

public class Test {
	public static void main(String[] args) {
		
		List<Person> list = Arrays.asList(
			new Person(1, "Ramesh", 45, 35000),
			new Person(2, "Bushan", 29, 22000),
			new Person(3, "Shankar", 33, 29000),
			new Person(4, "Chaitra", 32, 50000)
		);
		list.stream().sorted(Comparator.comparing(Person::getName)).forEach(System.out::println);
		System.out.println("****************************");
		list.stream().sorted(Comparator.comparing(Person::getName).reversed()).forEach(System.out::println);
	}
}

we will use comparing() to sort the String type which is provided by Comparator.

Example4.java

Let’s look at the soring using lambdas

public class Test {
	public static void main(String[] args) {
		
		List<Person> list = Arrays.asList(
			new Person(1, "Ramesh", 45, 35000),
			new Person(2, "Bushan", 29, 22000),
			new Person(3, "Shankar", 33, 29000),
			new Person(4, "Chaitra", 32, 50000)
		);
		list.stream().sorted((o1, o2) -> o1.getName().compareTo(o2.getName())).forEach(System.out::println);
		System.out.println("****************************");
		list.stream().sorted((o1, o2) -> o2.getName().compareTo(o1.getName())).forEach(System.out::println);
	}
}

Now let’s look at how to sort person’s salary using lambda’s

Example5.java

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

public class Test {
	public static void main(String[] args) {
		
		List<Person> list = Arrays.asList(
			new Person(1, "Ramesh", 45, 35000),
			new Person(2, "Bushan", 29, 22000),
			new Person(3, "Shankar", 33, 29000),
			new Person(4, "Chaitra", 32, 50000)
		);
		list.stream().sorted((e1, e2) -> (int)(e1.getSalary() - e2.getSalary())).forEach(System.out::println);
		System.out.println("****************************");
		list.stream().sorted((e1, e2) -> (int)(e2.getSalary() - e1.getSalary())).forEach(System.out::println);
	}
}

Similarly, we can use Comparator provided methods comparingLong(), comparingDouble() and comparingInt() to sort long, doubleand int values.