How to Reverse a String in Java Using Different Methods

String reversal is a fundamental problem frequently asked in coding interviews. we will explore multiple approaches to reverse a string in Java, with step-by-step explanations and practical code examples.

 

• 1. Using StringBuilder

Java provides StringBuilder, which has a built-in reverse() method to easily reverse a string.

 

public class ReverseStringExample {
public static void main (String args []){
String str = "CodeSpeedy";
StringBuilder sb = new StringBuilder(str);
sb.reverse(); // reverse the string
System.out.println("Reversed String: " sb);
}
}

OUTPUT
Reversed String: ydeepSedoC

2. Using a Character Array
In this method, we convert the string into a character array and swap the characters from start to end.

public class ReverseStringCharArray {
public static void main (String args []){
String str ="Java" ;
char[] charArray = str.toCharArray();
for (int i = 0, j = charArray.length - 1; i < j; i++, j--) {
char temp = charArray[i];
charArray[i] = charArray[j];
charArray[j] = temp;
}
String reversedStr = new String(charArray);
System.out.println("Reversed String: " + reversedStr);
}

OUTPUT
Reversed String: avaJ

• 3. Using Recursion 

  Recursion is a technique where a function calls itself until a base condition is met.
  

  public class ReverseStringRecursion {
  public static String reverse(String str) {
  if (str.isEmpty()) 
  return str;
  return reverse(str.substring(1)) + str.charAt(0);
  }
  
  public static void main(String[] args) {
  String str = "Hello";
  System.out.println("Reversed String: " + reverse(str));
  }
  }
  

  OUTPUT
  Reversed String: olleH

• 4. Using a for Loop 

  This method iterates through the string in reverse order and constructs the reversed string. 

  public class ReverseStringLoop {
  public static void main(String[] args) {
  String str = "World";
  String reversed = "";
  for (int i = str.length() - 1; i >= 0; i--) {
  reversed += str.charAt(i);
  }
  System.out.println("Reversed String: " + reversed);
  }
  }
  

   

  OUTPUT

  Reversed String: dlroW

• 5. Using Stack (LIFO – Last In First Out) 

  A stack follows the Last In, First Out (LIFO) principle. We push each character into the stack and then pop them to get the reversed string.
  

  import java.util.Stack;
  
  public class ReverseStringStack {
  public static void main(String[] args) {
  String str = "Code";
  Stack<Character> stack = new Stack<>();
   for (char c : str.toCharArray()) {
  stack.push(c);
  }
          
  String reversed = "";
  while (!stack.isEmpty()) {
  reversed += stack.pop();
  }
          
  System.out.println("Reversed String: " + reversed);
  }
  }
  

  OUTPUT
  Reversed String: edoC