Reverse a String Using Java Collections

Last Updated : 17 Mar 2025

In this article, we'll go through how to use the Java Collections Framework's reverse() function to reverse a string.

The use of Collections.reverse() to reverse a string in Java is demonstrated in the example below. The full process is as follows:

Using the String.toCharArray function, create an empty list of characters as well as fill it with the characters from the specified string ().
Use the reverse() function of java.util.Collections to reverse the list.
Use StringBuilder to transform the ArrayList into a String and then return the resultant string.

It is demonstrated in the following program:

File name: ReverseStringUsingCollections.java

// importing all packages
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.stream.Collectors;
 
class ReverseStringUsingCollections
{
    // function for reversing a string in Java using the `Collections.reverse()` method.
    public static String reverse(String s)
    {
        // returning the s if the s is null or empty
        if (s == null || s.equals("")) {
            return s;
        }
 
        // creating an empty list l of characters
        List<Character> l = new ArrayList<Character>();
 
        // pushing every character of the given string s into the list l
        for (char c1: s.toCharArray()) {
            l.add(c1);
        }
 
        // reversing the list 1 using `java.util.Collections` `reverse()`
        Collections.reverse(l);
 
        // converting the `ArrayList` into string s and returning it
        return l.stream().map(String::valueOf).collect(Collectors.joining());
    }
 
    public static void main(String args[])
    {
        String s = " Welcome to JavaTpoint ";
 
        // Strings are immutable
        s = reverse(s);
 
        System.out.println(" The string after reversing is:  " + s);
    }
}

Output:

The string after reversing is:   tniopTavaJ ot emocleW

In the solution above, ArrayList is first transformed into a StringBuilder, and then a string is created from a StringBuilder. Square brackets, commas, as well as a single space, can be taken out of an array list to turn it directly into a string. To do such, the code below uses String.replaceAll(). But this strategy is very ineffective and is to be avoided whenever possible.

File name: ReverseStringUsingCollections1.java

import java.util.List;
import java.util.ArrayList;
import java.util.Collections;
 
class ReverseStringUsingCollections1
{
    // function for reversing a string in Java using the `Collections.reverse()`
    public static String reverse(String s)
    {
        // returning if the string s is null or empty
        if (s == null || s.equals("")) {
            return s;
        }
 
        // creating an empty list l of characters and pushing every
        // character of the given string s into it
        List<Character> l = new ArrayList<Character>();
        for (char c1: s.toCharArray()) {
            l.add(c1);
        }
 
        // reversing the list using `java.util.Collections` `reverse()`
        Collections.reverse(l);
 
        // l.toString() is [t, h, g, I, l, e, D, e, i, h, c, e, T]
 
        // convert `l.toString()` to valid string
        return l.toString()
            .replaceAll("[,\\[\\]]", "")    // t h g I l e D   e I h c e T
            .replaceAll("  ", "@")          // t h g i l e D@ e i h c e T
            .replaceAll(" ", "")            // thgileD@eihceT
            .replaceAll("@", " ");          
    }
 
    public static void main(String args[])
    {
        String s = "Welcome to JavaTpoint";
 
        // Strings are immutable
        s = reverse(s);
 
        System.out.println(" The string after reversing is " + s);
    }
}

Output:

The string after reversing is tniopTavaJ ot emocleW

That was all there was to the reverse() method of the Java Collections Framework for a String.

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