Java API, recursive & iterative algorithm to reverse string (example)

Leave a Comment / By Yogesh / August 16, 2016

Given a String in java, reverse the String using standard java classes & recursive/iterative algorithm.
- e.g. reverse(“Lived”) = “deviL”
- reverse(“Star”) = “ratS”
We will reverse string using following methods.
- Reverse string using StringBuilder class.
- Reverse String using StringBuffer class.
- Java program to reverse String using iterative algorithm.
- Java program to reverse String using recursive algorithm.

Method 1: Reverse String using StringBuilder class

public static String reverseUsingStringBuilder(String inputString) {
        //inputString = "Lived"
    StringBuilder builder = new StringBuilder(inputString);
        //Output will be: deviL
    return builder.reverse().toString();
}

Method 2: Reverse String using StringBuffer class

public static String reverseUsingStringBuffer(String inputString) {
        //inputString = "Lived"
    StringBuffer builder = new StringBuffer(inputString);
        //Output will be: deviL
    return builder.reverse().toString();
}

Method 3: Java program to reverse string – iterative algorithm

//inputString = "Lived"
public static String iterative(String inputString) {
    if (null == inputString || inputString.length() == 0)
        return "";
 
    int length = inputString.length();
    char[] chInputArray = inputString.toCharArray();
    for (int index = 0; index < length / 2; index++) {
        char firstHalf = chInputArray[index];
        char secondHalf = chInputArray[length - index - 1];
 
        //swap
        chInputArray[index] = secondHalf;
        chInputArray[length - index - 1] = firstHalf;
    }
    return new String(chInputArray);
}//Reverse string of "Lived" is "deviL"

Method 4: Java program to reverse string – recursive algorithm

//inputString = "Lived"
public static String recursive(String inputString) {
 
    if (null == inputString || inputString.length() == 0)
        return "";
    return recursive(inputString.substring(1)) + inputString.charAt(0);
}//Reverse string of "Lived" is "deviL"

Logical flow to reverse string is shown Fig 1.

reverse string recursive algorithm — Fig 1: Reverse String using recursive algorithm: recursive(“Lived”) = deviL.

Complete Program to reverse a string in java:

package org.learn;
 
import java.util.Scanner;
 
public class StringReverse {
 
    public static String reverseUsingStringBuilder(String inputString) {
        StringBuilder builder = new StringBuilder(inputString);
        return builder.reverse().toString();
    }
 
    public static String reverseUsingStringBuffer(String inputString) {
        StringBuffer builder = new StringBuffer(inputString);
        return builder.reverse().toString();
    }
 
    public static String iterative(String inputString) {
         
        if (null == inputString || inputString.length() == 0)
            return "";
 
        int length = inputString.length();
        char[] chInputArray = inputString.toCharArray();
        for (int index = 0; index < length / 2; index++) {
             
            char firstHalf = chInputArray[index];
            char secondHalf = chInputArray[length - index - 1];
 
            // swap
            chInputArray[index] = secondHalf;
            chInputArray[length - index - 1] = firstHalf;
        }
        return new String(chInputArray);
    }
 
    public static String recursive(String inputString) {
 
        if (null == inputString || inputString.length() == 0)
            return "";
        return recursive(inputString.substring(1)) + inputString.charAt(0);
    }
 
    public static void main(String[] args) {
        try (Scanner scanner = new Scanner(System.in)) {
            System.out.printf("1. Enter input string : ");
            String input = scanner.next();
 
            String reverse = reverseUsingStringBuilder(input);
            System.out.printf("2. reverseUsingStringBuilder(\"%s\"): %s", input, reverse);
 
            reverse = reverseUsingStringBuffer(input);
            System.out.printf("\n3. reverseUsingStringBuffer(\"%s\"): %s", input, reverse);
 
            reverse = iterative(input);
            System.out.printf("\n4. iterative(\"%s\"): %s", input, reverse);
 
            reverse = recursive(input);
            System.out.printf("\n5. recursive(\"%s\"): %s", input, reverse);
        }
    }
}

Program output to reverse string in java:

Enter input string : Lived
reverseUsingStringBuilder("Lived"): deviL
reverseUsingStringBuffer("Lived"): deviL
iterative("Lived"): deviL
recursive("Lived"): deviL
 
Enter input string : Star
reverseUsingStringBuilder("Star"): ratS
reverseUsingStringBuffer("Star"): ratS
iterative("Star"): ratS
recursive("Star"): ratS