ReverseString.java

package com.thealgorithms.strings;

import java.util.Stack;

/**
 * Reverse String using different version
 */
public final class ReverseString {
 private ReverseString() {
 }

 /**
 * easiest way to reverses the string str and returns it
 *
 * @param str string to be reversed
 * @return reversed string
 */
 public static String reverse(String str) {
 return new StringBuilder(str).reverse().toString();
 }

 /**
 * second way to reverses the string str and returns it
 *
 * @param str string to be reversed
 * @return reversed string
 */
 public static String reverse2(String str) {
 if (str == null || str.isEmpty()) {
 return str;
 }

 char[] value = str.toCharArray();
 for (int i = 0, j = str.length() - 1; i < j; i++, j--) {
 char temp = value[i];
 value[i] = value[j];
 value[j] = temp;
 }
 return new String(value);
 }

 /**
 * Reverse version 3 the given string using a StringBuilder.
 * This method converts the string to a character array,
 * iterates through it in reverse order, and appends each character
 * to a StringBuilder.
 *
 * @param string The input string to be reversed.
 * @return The reversed string.
 */
 public static String reverse3(String string) {
 if (string.isEmpty()) {
 return string;
 }
 char[] chars = string.toCharArray();
 StringBuilder sb = new StringBuilder();
 for (int i = string.length() - 1; i >= 0; i--) {
 sb.append(chars[i]);
 }
 return sb.toString();
 }
 /**
 * Reverses the given string using a stack.
 * This method uses a stack to reverse the characters of the string.
 * @param str The input string to be reversed.
 * @return The reversed string.
 */
 public static String reverseStringUsingStack(String str) {
 // Check if the input string is null
 if (str == null) {
 throw new IllegalArgumentException("Input string cannot be null");
 }
 Stack<Character> stack = new Stack<>();
 StringBuilder reversedString = new StringBuilder();
 // Check if the input string is empty
 if (str.isEmpty()) {
 return str;
 }
 // Push each character of the string onto the stack
 for (char ch : str.toCharArray()) {
 stack.push(ch);
 }
 // Pop each character from the stack and append to the StringBuilder
 while (!stack.isEmpty()) {
 reversedString.append(stack.pop());
 }
 return reversedString.toString();
 }

 /**
 * Reverse the String using Recursion
 * @param str string to be reversed
 * @return reversed string
 */
 public static String reverseStringUsingRecursion(String str) {
 if (str.isEmpty()) {
 return str;
 } else {
 return reverseStringUsingRecursion(str.substring(1)) + str.charAt(0);
 }
 }
}