Reverse String in Java.

How to Reverse String in Java.


Reverse String in Java. String can be reversed using Iterative and Recursive approach. We will Reverse a String using Recursion and using loop. For reversing a String we should not use any inbuilt methods.

Input:      "Reverse String"
Output:   "gnirtS esreveR"

Input:      "HELLO"
Output:   "OLLEH"

Input:      "123 abc"
Output:   "cba 321"

Algorithm



1. Reverse a String using Loop

STEP 1: Initialize i = string.length()-1 as we need to read the characters of String from back.
STEP 2: Iterate till i>=0, that is to read all the characters of array till first character present at index 0.
STEP 3: Decrement i-- at each iteration as we are printing backwards.
STEP 4: Using string.charAt(i), method, pick each character of String and Print it.
 
public class ReverseStringInJava {
 public static void main(String[] args) {  
  reverseString("Reverse String");
 }
 
 public static void reverseString(String str){
  for (int i = str.length()-1; i >= 0; i--) {
   System.out.print(str.charAt(i));
  }
 }
}
 

2. Reverse a String using Recursion

In this approach, we will Reverse a String using recursion. 

In each Recursive step, we will pick character at index 0 and pass the remaining Substring to next Recursive call.
Repeat until substring length is not equal to 0. When substring length is == 0, Return String.


 
public class ReverseStringInJava {
 public static void main(String[] args) {  
  System.out.println(reverseString("JavaByPatel"));
 }

 public static String reverseString(String str) {     
  if (str.length() == 0) 
   return str;

  return reverseWord(str.substring(1)) + str.charAt(0);
 }
}
 

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Enjoy !!!! 

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