Java Program to Reverse a String (5 ways)

In this post, we will write a Java Program to reverse a given String. We show you 5 different ways we can reverse the String.

5 Methods to Reverse a String

1. Reverse With String Concat

public static final String reverseWithStringConcat(String string) {
    String output = new String();
    for (int i = (string.length() - 1); i >= 0; i--) {
          output += (string.charAt(i));
     }
 
     display(string,output);
     return output;
}

2. Reverse With StringBuilder

public static final String reverseWithStringBuilder(String string) {
    final StringBuilder builder = new StringBuilder();
    for (int i = (string.length() - 1); i >= 0; i--) {
         builder.append(string.charAt(i));
    }
    display(string,builder.toString());
    return builder.toString();
}

3. Reverse With StringBuilder Built-in Method - reverse()

public static final String reverseWithStringBuilderBuiltinMethod(String string) {
    final StringBuilder builder = new StringBuilder(string);
    display(string, builder.reverse().toString());
    return builder.reverse().toString();
}

4. Reverse With Swapping characters

public static final String reverseWithSwaps(String string) {
    final char[] array = string.toCharArray();
    final int length = array.length - 1;
    final int half = (int) Math.floor(array.length / 2);

    char c;
    for (int i = length; i >= half; i--) {
          c = array[length - i];
          array[length - i] = array[i];
          array[i] = c;
    }
    display(string, String.valueOf(array));
    return String.valueOf(array);
}

5. Reverse with XOR(^) operator

public static final String reverseWithXOR(String string) {
    final char[] array = string.toCharArray();
    final int length = array.length;
    final int half = (int) Math.floor(array.length / 2);

    for (int i = 0; i < half; i++) {
         array[i] ^= array[length - i - 1];
         array[length - i - 1] ^= array[i];
         array[i] ^= array[length - i - 1];
    }
    display(string, String.valueOf(array));
    return String.valueOf(array);
}

Complete Program

package com.javaguides.strings.examples;

/**
 * 5 ways to reverse a String in Java
 * @author javaguides.net
 *
 */
public class ReverseString5Ways {

    public static void main(String[] args) {
        reverseWithStringConcat("javaguides");
        reverseWithStringBuilder("javaguides");
        reverseWithStringBuilderBuiltinMethod("javaguides");
        reverseWithSwaps("javaguides");
        reverseWithXOR("javaguides");
    }

    public static final String reverseWithStringConcat(String string) {
        String output = new String();
        for (int i = (string.length() - 1); i >= 0; i--) {
            output += (string.charAt(i));
        }

        display(string, output);
        return output;
    }

    public static final String reverseWithStringBuilder(String string) {
        final StringBuilder builder = new StringBuilder();
        for (int i = (string.length() - 1); i >= 0; i--) {
            builder.append(string.charAt(i));
        }
        display(string, builder.toString());
        return builder.toString();
    }

    public static final String reverseWithStringBuilderBuiltinMethod(String string) {
        final StringBuilder builder = new StringBuilder(string);
        display(string, builder.reverse().toString());
        return builder.reverse().toString();
    }

    public static final String reverseWithSwaps(String string) {
        final char[] array = string.toCharArray();
        final int length = array.length - 1;
        final int half = (int) Math.floor(array.length / 2);

        char c;
        for (int i = length; i >= half; i--) {
            c = array[length - i];
            array[length - i] = array[i];
            array[i] = c;
        }
        display(string, String.valueOf(array));
        return String.valueOf(array);
    }

    public static final String reverseWithXOR(String string) {
        final char[] array = string.toCharArray();
        final int length = array.length;
        final int half = (int) Math.floor(array.length / 2);

        for (int i = 0; i < half; i++) {
            array[i] ^= array[length - i - 1];
            array[length - i - 1] ^= array[i];
            array[i] ^= array[length - i - 1];
        }
        display(string, String.valueOf(array));
        return String.valueOf(array);
    }


    private static final void display(String original, String reverse) {
        System.out.println(original);
        System.out.println(reverse);
        System.out.println("----------------------------");
    }
}

Output:

javaguides
sediugavaj
----------------------------
javaguides
sediugavaj
----------------------------
javaguides
sediugavaj
----------------------------
javaguides
sediugavaj
----------------------------
javaguides
sediugavaj
----------------------------

From above 5 different approaches, prefer StringBuilder built-in reverse() method for better performance.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

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