Java 8 – Sorting Arrays in Ascending and Descending order

In this article, we will discuss how to sort Arrays in both ascending and descending order of Integer, String and Employee objects

1. Sorting Arrays in Ascending order :

1.1 Sorting Integer[] Arrays in Ascending order :

AscendingOrderSortingOfIntegerArraysInJava8.java

package in.bench.resources.arrays.sorting;

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

public class AscendingOrderSortingOfIntegerArraysInJava8 {

	public static void main(String[] args) {

		// sample Integer[] array
		Integer[] intArray = {
				1975,
				2003,
				1979,
				1992,
				1983,
				1999,
				1987
		};


		// before sorting
		System.out.println("Before sorting - Integer[] Arrays\n");
		for(Integer iValue : intArray) {
			System.out.println(iValue);
		}


		// sorting Integer[] arrays in ascending order
		Arrays.sort(intArray, Comparator.naturalOrder());


		// after sorting
		System.out.println("\nAfter sorting in Ascending-order - Integer[] Arrays\n");
		for(Integer iValue : intArray) {
			System.out.println(iValue);
		}
	}
}

Output:

Before sorting - Integer[] Arrays

1975
2003
1979
1992
1983
1999
1987

After sorting in Ascending-order - Integer[] Arrays

1975
1979
1983
1987
1992
1999
2003

1.2 Sorting String[] Arrays in Ascending order :

AscendingOrderSortingOfStringArraysInJava8.java

package in.bench.resources.arrays.sorting;

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

public class AscendingOrderSortingOfStringArraysInJava8 {

	public static void main(String[] args) {

		// sample String[] array
		String[] strArray = {
				"Clive",
				"Kapil",
				"Allan",
				"Imran",
				"Arjuna",
				"Steve",
				"Ricky"
		};


		// before sorting
		System.out.println("Before sorting - String[] Arrays\n");
		for(String str : strArray) {
			System.out.println(str);
		}


		// sorting String[] arrays in ascending order
		Arrays.sort(strArray, Comparator.naturalOrder());


		// after sorting
		System.out.println("\nAfter sorting in Ascending-order - String[] Arrays\n");
		for(String str : strArray) {
			System.out.println(str);
		}
	}
}

Output:

Before sorting - String[] Arrays

Clive
Kapil
Allan
Imran
Arjuna
Steve
Ricky

After sorting in Ascending-order - String[] Arrays

Allan
Arjuna
Clive
Imran
Kapil
Ricky
Steve

1.3 Sorting Employee[] Arrays in Ascending order :

  • In Java 8, Arrays.sort() method accepts 2 input-arguments where,
    • 1st argument is the original/actual arrays to be sorted
    • 2nd argument is the Comparator object for natural order sorting of first name using method reference as shown in the below example
  • Employee class consists of 4 member variables with
    • 4-argument parameterized constructor
    • setters and getters
    • overriding toString() method
    • removed for brevity

Employee.java

package in.bench.resources.arrays.sorting;

public class Employee {

	// member variables
	private int id;
	private String firstName;
	private String lastName;
	private float salary;

	// 4-argument parameterized constructor

	// getters & setters

	// toString() method
}

AscendingOrderSortingOfEmployeeArraysInJava8.java

package in.bench.resources.arrays.sorting;

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

public class AscendingOrderSortingOfEmployeeArraysInJava8 {

	public static void main(String[] args) {

		// sample Employee[] array
		Employee[] employees = new Employee[]{
				new Employee(1001, "Suresh", "Krishna", 25000.00f),
				new Employee(1002, "Mani", "Ratnam", 58000.00f),
				new Employee(1003, "Balu", "Mahendra", 46000.00f),
				new Employee(1004, "Venkat", "Prabhu", 35000.00f),
				new Employee(1005, "Lokesh", "Kanagaraj", 75000.00f)
		};


		// before sorting
		System.out.println("Before sorting - Employee[] Arrays\n");
		for(Employee emp : employees) {
			System.out.println(emp);
		}


		// sorting Employee[] arrays in ascending order
		Arrays.sort(employees, Comparator.comparing(Employee::getFirstName));


		// after sorting
		System.out.println("\nAfter sorting in Ascending-order of first name"
				+ " - Employee[] Arrays\n");
		for(Employee emp : employees) {
			System.out.println(emp);
		}
	}
}

Output:

Before sorting - Employee[] Arrays

Employee [id=1001, firstName=Suresh, lastName=Krishna, salary=25000.0]
Employee [id=1002, firstName=Mani, lastName=Ratnam, salary=58000.0]
Employee [id=1003, firstName=Balu, lastName=Mahendra, salary=46000.0]
Employee [id=1004, firstName=Venkat, lastName=Prabhu, salary=35000.0]
Employee [id=1005, firstName=Lokesh, lastName=Kanagaraj, salary=75000.0]

After sorting in Ascending-order of first name - Employee[] Arrays

Employee [id=1003, firstName=Balu, lastName=Mahendra, salary=46000.0]
Employee [id=1005, firstName=Lokesh, lastName=Kanagaraj, salary=75000.0]
Employee [id=1002, firstName=Mani, lastName=Ratnam, salary=58000.0]
Employee [id=1001, firstName=Suresh, lastName=Krishna, salary=25000.0]
Employee [id=1004, firstName=Venkat, lastName=Prabhu, salary=35000.0]

2. Sorting Arrays in Descending order :

2.1 Sorting Integer[] Arrays in Descending order :

DescendingOrderSortingOfIntegerArraysInJava8.java

package in.bench.resources.arrays.sorting;

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

public class DescendingOrderSortingOfIntegerArraysInJava8 {

	public static void main(String[] args) {

		// sample Integer[] array
		Integer[] intArray = {
				1975,
				2003,
				1979,
				1992,
				1983,
				1999,
				1987
		};


		// before sorting
		System.out.println("Before sorting - Integer[] Arrays\n");
		for(Integer iValue : intArray) {
			System.out.println(iValue);
		}


		// sorting Integer[] arrays in descending order
		Arrays.sort(intArray, Comparator.reverseOrder());


		// after sorting
		System.out.println("\nAfter sorting in Descending-order - Integer[] Arrays\n");
		for(Integer iValue : intArray) {
			System.out.println(iValue);
		}
	}
}

Output:

Before sorting - Integer[] Arrays

1975
2003
1979
1992
1983
1999
1987

After sorting in Descending-order - Integer[] Arrays

2003
1999
1992
1987
1983
1979
1975

2.2 Sorting String[] Arrays in Descending order :

DescendingOrderSortingOfStringArraysInJava8.java

package in.bench.resources.arrays.sorting;

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

public class DescendingOrderSortingOfStringArraysInJava8 {

	public static void main(String[] args) {

		// sample String[] array
		String[] strArray = {
				"Clive",
				"Kapil",
				"Allan",
				"Imran",
				"Arjuna",
				"Steve",
				"Ricky"
		};


		// before sorting
		System.out.println("Before sorting - String[] Arrays\n");
		for(String str : strArray) {
			System.out.println(str);
		}


		// sorting String[] arrays in descending order
		Arrays.sort(strArray, Comparator.reverseOrder());


		// after sorting
		System.out.println("\nAfter sorting in Descending-order - String[] Arrays\n");
		for(String str : strArray) {
			System.out.println(str);
		}
	}
}

Output:

Before sorting - String[] Arrays

Clive
Kapil
Allan
Imran
Arjuna
Steve
Ricky

After sorting in Descending-order - String[] Arrays

Steve
Ricky
Kapil
Imran
Clive
Arjuna
Allan

2.3 Sorting Employee[] Arrays in Descending order :

  • In Java 8, Arrays.sort() method accepts 2 input-arguments where,
    • 1st argument is the original/actual arrays to be sorted
    • 2nd argument is the Comparator object for reverse order sorting of first name using method reference as shown in the below example
  • Employee class consists of 4 member variables with
    • 4-argument parameterized constructor
    • setters and getters
    • overriding toString() method
    • removed for brevity

Employee.java

package in.bench.resources.arrays.sorting;

public class Employee {

	// member variables
	private int id;
	private String firstName;
	private String lastName;
	private float salary;

	// 4-argument parameterized constructor

	// getters & setters

	// toString() method
}

DescendingOrderSortingOfEmployeeArraysInJava8.java

package in.bench.resources.arrays.sorting;

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

public class DescendingOrderSortingOfEmployeeArraysInJava8 {

	public static void main(String[] args) {

		// sample Employee[] array
		Employee[] employees = new Employee[]{
				new Employee(1001, "Suresh", "Krishna", 25000.00f),
				new Employee(1002, "Mani", "Ratnam", 58000.00f),
				new Employee(1003, "Balu", "Mahendra", 46000.00f),
				new Employee(1004, "Venkat", "Prabhu", 35000.00f),
				new Employee(1005, "Lokesh", "Kanagaraj", 75000.00f)
		};


		// before sorting
		System.out.println("Before sorting - Employee[] Arrays\n");
		for(Employee emp : employees) {
			System.out.println(emp);
		}


		// sorting Employee[] arrays in descending order
		Arrays.sort(employees, Comparator.comparing(Employee::getFirstName).reversed());


		// after sorting
		System.out.println("\nAfter sorting in Descending-order of first name"
				+ " - Employee[] Arrays\n");
		for(Employee emp : employees) {
			System.out.println(emp);
		}
	}
}

Output:

Before sorting - Employee[] Arrays

Employee [id=1001, firstName=Suresh, lastName=Krishna, salary=25000.0]
Employee [id=1002, firstName=Mani, lastName=Ratnam, salary=58000.0]
Employee [id=1003, firstName=Balu, lastName=Mahendra, salary=46000.0]
Employee [id=1004, firstName=Venkat, lastName=Prabhu, salary=35000.0]
Employee [id=1005, firstName=Lokesh, lastName=Kanagaraj, salary=75000.0]

After sorting in Descending-order of first name - Employee[] Arrays

Employee [id=1004, firstName=Venkat, lastName=Prabhu, salary=35000.0]
Employee [id=1001, firstName=Suresh, lastName=Krishna, salary=25000.0]
Employee [id=1002, firstName=Mani, lastName=Ratnam, salary=58000.0]
Employee [id=1005, firstName=Lokesh, lastName=Kanagaraj, salary=75000.0]
Employee [id=1003, firstName=Balu, lastName=Mahendra, salary=46000.0]

Note: we need to convert primitive int data-type to Integer wrapper-type by auto-boxing feature introduced in Java 1.5 version, when we pass Comparator object as 2nd argument for reverse order sorting

Hope, you found this article very helpful. If you have any suggestion or want to contribute any other way or tricky situation you faced during Interview hours, then share with us. We will include that code here.

References:

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