How to reverse a list in Java

admin November 8, 2020October 9, 2021 0 Comments collections, how to reverse a list in java, reverse list java 8

In this tutorial, we’re going to see how we can reverse the elements of a list in Java. If the list can be changed, Java offers a simple method in the class java.util.Collections. For example, if we have this list:

List: 1 2 3 4 5 6 7 8 9 10

In the result we can have:

List: 10 9 8 7 6 5 4 3 2 1

Reverse the list itself

If the list itself may be changed, reversing the order with the method Collections.reverse() can be very easy:

import java.util.*;

public class Main
{
    public static void main(String[] args) 
    {
        List<String> names = new ArrayList<>(Arrays.asList("Alex", "Thomas", "Emily", "Bob", "Jean"));
        
        Collections.reverse(names);
        
        System.out.println(names);
    }
}

Output:

[Jean, Bob, Emily, Thomas, Alex]

If you don’t want the original list to be changed, see the example below.

Insert elements into new list in reverse order

If you do not want to change the original list or if it is unchangeable, simply create a new list with the same size. The naive simple solution could look like this:

import java.util.*;

public class Main
{
    public static void main(String[] args) 
    {
        List<String> names = new ArrayList<>(Arrays.asList("Alex", "Thomas", "Emily", "Bob", "Jean"));
        
        List<String> inverse = new ArrayList<>(names.size());
        
        for (int i = names.size()-1; i >= 0; i--) 
        {
            inverse.add(names.get(i));
        }
        
        System.out.println(inverse);
    }
}

Output: