Reverse a string in java

Let’s learn to reverse a string in java.

Reverse a string in java

In java, a string can be reversed in ‘n’ number of ways. Let’s learn following ways to reverse a string,

• using for loop
• word by word
• without using function
• using recursion

Reverse a string in java using for loop

To reverse a string, variable b is iterated through for loop from b = length of the given string to b greater than 0.

Then in the next step character of string is printed at index (a – 1). Lastly print reversed string.

Here’s the program to reverse string using a for loop,

import java.util.Scanner;

public class ReverseStringForLoop 
{
   public static void main(String[] args) 
   {
      Scanner sc = new Scanner(System.in);
      System.out.print("Please enter a string to reverse: ");
      String strInput = sc.nextLine();    
      System.out.println("Reversed string using for loop '" + strInput + "' is: "); 
      for(int b = strInput.length(); b > 0; --b)
      {
         System.out.print(strInput.charAt(b - 1)); 
      }
      sc.close();
   }
}

Output:

Please enter a string to reverse: helloworld
Reversed string using for loop ‘helloworld’ is: dlrowolleh

Please enter a string to reverse: flowerbrackets
Reversed string using for loop ‘flowerbrackets’ is: stekcarbrewolf

how to reverse a string in java word by word:

Here to reverse string word by word, first read user entered string using scanner class.

User entered string is stored in String variable. Then this string variable is converted to character array using toCharArray() method of class String.

Also read – java remove character from string

In the next step two for loops is used. First for loop iterates variable ‘a’ from 0 to a < length of given character array.

Then if chArray[a] != ‘ ‘ add chArray[0] to string strWord. Next until we get space, if block adds characters to string strWord.

Moving on, else block reverses the word if we get space. Lastly second for loop reverses last word.

Here’s how to reverse a string in java word by word,

import java.util.Scanner;

public class ReverseWordByWord 
{
   public static void main(String[] args) 
   {
      String strWord = "";
      Scanner sc = new Scanner(System.in);
      System.out.print("Please enter a string: ");
      String strGiven = sc.nextLine();     
      char[] chArray = strGiven.toCharArray();
      System.out.println("Reversed string word by word: ");
      for(int a = 0; a < (chArray.length); a++)
      {
         if(chArray[a] != ' ')
         {
            strWord = strWord + chArray[a];
         }
         else
         {
            for(int b = strWord.length(); b > 0; b--)
            {
               System.out.print(strWord.charAt(b - 1));       
            }
            System.out.print(" ");
            strWord = "";
         }
      }
      for(int b = strWord.length(); b > 0; b--)
      {
         System.out.print(strWord.charAt(b - 1));       
      }
      sc.close();
   }
}

Output:

Please enter a string: hello world java
Reversed string word by word: olleh dlrow avaj

Please enter a string: flower brackets java
Reversed string word by word: rewolf stekcarb avaj

without using reverse function

Let’s see java program,

import java.util.Scanner;

public class ReverseWithoutFunction 
{
   public static void main(String[] args) 
   {
      Scanner sc = new Scanner(System.in);
      System.out.println("Please enter a string: ");
      String strInput = sc.nextLine();
      int len = strInput.length();
      String strReverse = "";
      System.out.println("Reversed string without using function: ");
      for(int a = len - 1; a >= 0; a--)
      {
         strReverse = strReverse + strInput.charAt(a);
      }
      System.out.println(strReverse);
      sc.close();
   }
}

Output:

Please enter a string: flowerbrackets
Reversed string without using function: stekcarbrewolf

Please enter a string: helloworld
Reversed string without using function: dlrowolleh

using recursion

Recursive function is one which calls itself. Let’s reverse a string in java using recursion,

import java.util.Scanner;

public class ReverseUsingRecursion 
{
   String reverseRecursive(String str)
   {
      if(str.length() == 0)
          return " ";
      return str.charAt(str.length() - 1) + reverseRecursive(str.substring(0, str.length() - 1));
   }

   public static void main(String[] args) 
   {
      ReverseUsingRecursion obj = new ReverseUsingRecursion();
      Scanner sc = new Scanner(System.in);
      System.out.print("Please enter a string: ");
      String strInput = sc.nextLine();    
      System.out.println("Reverse string using recursion: " + obj.reverseRecursive(strInput));
      sc.close();
   }
}

Output:

Please enter a string: helloworld
Reverse string using recursion: dlrowolleh

Please enter a string: java
Reverse string using recursion: avaj