1. Introduction

Often in programming, there is a need to sort collections in reverse order. Java provides the Comparator interface, which is powerful and flexible. One of the utility methods it provides is reverseOrder(), which returns a comparator that imposes the reverse of the natural ordering on a collection of objects that implement the Comparable interface. In this post, we will see how to use this method to sort a list of integers in descending order.

2. Program Steps

1. Create a list of integers.

2. Use the reverseOrder() method from the Comparator interface to get a comparator for reverse order.

3. Sort the list using the sort() method and the obtained comparator.

4. Print the sorted list.

3. Code Program

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

public class ReverseOrderComparatorDemo {

    public static void main(String[] args) {
        // Create a list of integers
        List<Integer> numbers = Arrays.asList(3, 1, 4, 1, 5, 9, 2, 6, 5);

        System.out.println("Original list: " + numbers);

        // Sort the list in descending order
        numbers.sort(Comparator.reverseOrder());

        System.out.println("Sorted in descending order: " + numbers);
    }
}

Output:

Original list: [3, 1, 4, 1, 5, 9, 2, 6, 5]
Sorted in descending order: [9, 6, 5, 5, 4, 3, 2, 1, 1]

4. Step By Step Explanation

1. We start by creating a list of integers.

2. Next, we print the original list to show the initial order of elements.

3. We then use the sort() method on the list, passing Comparator.reverseOrder() as the argument. The reverseOrder() method is a static method provided by the Comparator interface. It returns a comparator that imposes the reverse of the natural ordering on a collection of objects that implement the Comparable interface.

4. Finally, we print the sorted list, which is now in descending order.

This approach is convenient and clean, allowing for a concise way to sort collections in reverse order without having to define a custom comparator.