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. To do that we use StringBuilder, StringBuffer and String class. Below are few examples.

Using append method of StringBuilder class

In java, String class does not have reverse() method. So we must convert the input string to StringBuilder using the append method of StringBuilder class.

Then print the reversed string.

import java.util.Scanner;

public class StringReverse 
{
   public static void main(String[] args) 
   {
      System.out.println("Please enter a string to reverse : ");
      Scanner sc = new Scanner(System.in);
      String strInput = sc.nextLine();
      StringBuilder sb = new StringBuilder();
      // appending string into StringBuilder sb 
      sb.append(strInput);
      // reversing StringBuilder sb 
      sb = sb.reverse();
      // printing reversed string 
      System.out.println(sb);
      sc.close();
   }
}

Output:

Please enter a string to reverse : flower brackets
stekcarb rewolf

Convert String into Bytes

First we create a temporary byte array equal to length of given string. Next we create temporary byte array in which we store bytes which we get using getBytes() method in reverse order.

Also read – sort string array java

getBytes() method returns the resultant byte array. Lastly a new String object is created to store the output.

public class StringReversal 
{
   public static void main(String[] args) 
   {
      String strInput = "Flowerbrackets";
      // convert string into bytes using getBytes() method
      byte strByte[] = strInput.getBytes();
      byte output[] = new byte[strByte.length];
      // storing output in reverse order
      for(int a = 0; a < strByte.length; a++)
      {
         output[a] = strByte[strByte.length - a - 1];
      }
      System.out.println("Output : " + new String(output));
   }
}

Output :

Output : stekcarbrewolF

Convert String to character array

In this java program, we first convert string to character array using String class method toCharArray() and print char one by one.

public class ReversalString 
{
   public static void main(String[] args) 
   {
      String strInput = "FlowerBrackets";
      // converting string to character array using toCharArray method
      char demo[] = strInput.toCharArray();
      for(int a = demo.length - 1; a >= 0; a--)
      {
         System.out.print(demo[a]);
      }
   }
}

Output :

stekcarBrewolF

Convert input string to character array using toCharArray() method

Here in this java program we set left index = 0 and right index = length of input string minus 1. Next we swap characters from start to end one by one.

In the for loop we increase left index and right index by one and continue up till <= right.

public class StringReverseJava 
{
   public static void main(String[] args) 
   {
      String strInput = "Flower Brackets";
      // converting strInput into character array using toCharArray()
      char demo[] = strInput.toCharArray();
      // setting left index and right index equal to 0
      int left, right = 0;
      // setting length of string - 1
      right = demo.length - 1;

      for(left = 0; left < right ; left++ , right--)
      {
         // swapping characters from start index with last index 
and scanning one by one.
         char temp = demo[left];
         demo[left] = demo[right];
         demo[right] = temp;
      }

      for(char ch : demo)
         System.out.print(ch);
      System.out.println();
   }
}

Output :

stekcarB rewolF

Using ListIterator

In this java program we convert input string to character array using toCharArray() method. Next we add characters of the array into ArrayList object.

In java we have reverse method of Collections class. This method takes list object to reverse list. Lastly we pass LinkedList object which is type of list of characters,

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.ListIterator;

public class StringReverser 
{
   public static void main(String[] args) 
   {
      String strInput = "Flower Brackets";
      // copying String to ArrayList object
      char[] demo = strInput.toCharArray();
      List<Character> test = new ArrayList<>();

      for(char ch : demo)
         test.add(ch);

      // reverse() method takes "test" object, to reverse the list 
      Collections.reverse(test);
      // creating ListIterator object using the listIterator() method on LinkedList object
      ListIterator li = test.listIterator();
      // iterate over the list
      while(li.hasNext())
      {
         // printing it one by one
         System.out.print(li.next());
      }
   }
}

Output :

stekcarB rewolF

Bottom Line : Above examples on how to reverse a string in java can be used in java based on project requirement.