Java Collections reverse()

In this guide, you will learn about the Collections reverse() method in Java programming and how to use it with an example.

1. Collections reverse() Method Overview

Definition:

The reverse() method of the Collections class in Java is used to reverse the order of elements in a specified list.

Syntax:

Collections.reverse(List<?> list)

Parameters:

list: The list whose elements are to be reversed.

Key Points:

- After executing the method, the list provided will be modified such that the order of its elements is reversed.

- It throws UnsupportedOperationException if the specified list or its list-iterator doesn't support the set operation.

- This is a very efficient method to reverse a list as it doesn't involve any copying of elements.

2. Collections reverse() Method Example

import java.util.*;

public class CollectionsReverseExample {
    public static void main(String[] args) {
        List<Integer> numbers = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5));

        // Reversing the list
        Collections.reverse(numbers);
        System.out.println("Reversed list: " + numbers);
    }
}

Output:

Reversed list: [5, 4, 3, 2, 1]

Explanation:

In the provided example, we create a list of integers from 1 to 5. We then use the reverse() method to reverse the order of its elements and print the reversed list.