In Java, you use arrays to store a collection of variables (with the same data type) in a single variable.

In many cases, the values stored in an array appear in a random order. Using the Arrays class in Java, you have access to various methods you can use to manipulate arrays.

One of the methods we'll be using from the Arrays class is the sort() method which sorts an array in ascending order.

We'll also see how to sort an array in descending order using the reverseOrder() method from the Collections class in Java.

How to Sort an Array in Ascending Order in Java Using Arrays.sort()

In this section, we'll see an example on how we can use the sort() method to sort an array in ascending order.

import java.util.Arrays;

class ArraySort {
    public static void main(String[] args) {
        int[] arr = { 5, 2, 1, 8, 10 };
        Arrays.sort(arr);
        
        for (int values : arr) {
            System.out.print(values + ", ");
            // 1, 2, 5, 8, 10,
        }
    }
}

The first thing we did in the example above was to import the Arrays class: import java.util.Arrays;. This give us access to all the methods of the Arrays class.

We then created an array with numbers in a random order: int[] arr = { 5, 2, 1, 8, 10 };.

In order to sort this array in ascending order, we passed in the array as parameter to the sort() method: Arrays.sort(arr);.

Note that the Arrays class was written first before accessing the sort() method using dot notation.

Lastly, we looped through and printed the array in the console. The result was a sorted array: 1, 2, 5, 8, 10.

In the next section, we'll talk about sorting an array in descending order.

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How to Sort an Array in Descending Order in Java Using Collections.reverseOrder()

To sort an array in descending order, we use the reverseOrder() which we can access from the Collections class.

We'll still make use of Arrays.sort();, but in this example, it'll take in two parameters – the array to be sorted and Collections.reverseOrder().

Here's an example:

import java.util.Arrays;
import java.util.Collections;

class ArraySort {
    public static void main(String[] args) {
        Integer[] arr = { 5, 2, 1, 8, 10 };
        Arrays.sort(arr, Collections.reverseOrder());
        
        for (int values : arr) {
            System.out.print(values + ", ");
            // 10, 8, 5, 2, 1,
        }
    }
}

First things first, we imported the Arrays and Collections classes because we'll be making use the methods provided by the classes.

We then created an array of numbers in random order: Integer[] arr = { 5, 2, 1, 8, 10 };.  You'll notice that we used Integer[] instead of int[] like we did in the last example – the latter would throw an error.

To sort the array in descending order, we did this: Arrays.sort(arr, Collections.reverseOrder());.

The first parameter is the array arr which will be sorted in ascending order. The second parameter – Collections.reverseOrder() – will then reverse the order of the sorted array so it is arranged in descending order.

When looped through and printed, the array would look like this: 10, 8, 5, 2, 1.

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Summary

In this article, we talked about sorting arrays in Java. Arrays can be sorted in ascending or descending order.

We can sort arrays in ascending order using the sort() method which can be accessed from the Arrays class. The sort() method takes in the array to be sorted as a parameter.

To sort an array in descending order, we used the reverseOrder() method provided by the Collections class. This is passed in as a second parameter in the sort() method so that the sorted array can be rearranged in descending order.

Happy coding!