Reverse a string in Java

This article discusses 5 different ways to reverse a string in Java with examples.
Examples:

Prerequisite : String vs StringBuilder vs StringBuffer in Java

Following are some interesting facts about String and StringBuffer classes :
1. Objects of String are immutable.
2. String class in Java does not have reverse() method, however StringBuilder class has built in reverse() method.
3. StringBuilder class do not have toCharArray() method, while String class does have toCharArray() method.

1. Converting String into Bytes: getBytes() method is used to convert the input string into bytes[].
   Method:
   

   1. Create a temporary byte[]  of length equal 
      to the length of the input string.
   2. Store the bytes (which we get by using 
      getBytes() method) in reverse order into 
      the temporary byte[] .
   3. Create a new String abject using byte[] to
      store result.
   

   // Java program to ReverseString using ByteArray. import java.lang.*; import java.io.*; import java.util.*;    // Class of ReverseString class ReverseString {     public static void main(String[] args)     {         String input = "GeeksforGeeks";            // getBytes() method to convert string          // into bytes[].         byte [] strAsByteArray = input.getBytes();            byte [] result =                     new byte [strAsByteArray.length];            // Store result in reverse order into the         // result byte[]         for (int i = 0; i<strAsByteArray.length; i++)             result[i] =               strAsByteArray[strAsByteArray.length-i-1];            System.out.println(new String(result));     } }

   Output:

   skeeGrofskeeG
   

2. Using built in reverse() method of the StringBuilder class: String class does not have reverse() method, we need to convert the input string to StringBuilder, which is achieved by using the append method of StringBuilder. After that, print out the characters of the reversed string by scanning from the first till the last index.

   // Java program to ReverseString using StringBuilder import java.lang.*; import java.io.*; import java.util.*;    // Class of ReverseString class ReverseString {     public static void main(String[] args)     {         String input = "Geeks for Geeks";            StringBuilder input1 = new StringBuilder();            // append a string into StringBuilder input1         input1.append(input);            // reverse StringBuilder input1         input1 = input1.reverse();            // print reversed String         System.out.println(input1);     } }

   Output:

   skeeG rof skeeG
   

3. Converting String to character array: The user input the string to be reversed.
   Method:

   1. First, convert String to character array
      by using the built in Java String class 
      method toCharArray().
   2. Then, scan the string from end  to start, 
      and print the character one by one.
   

   // Java program to Reverse a String  by // converting string to characters  one // by one import java.lang.*; import java.io.*; import java.util.*;    // Class of ReverseString class ReverseString {     public static void main(String[] args)     {         String input = "GeeksForGeeks";            // convert String to character array         // by using toCharArray         char[] try1 = input.toCharArray();            for (int i = try1.length-1; i>=0; i--)             System.out.print(try1[i]);     } }

   Output:

   skeeGrofskeeG
   

4. Convert the input string into character array by using the toCharArray(): Convert the input string into character array by using the toCharArray() – built in method of the String Class. Then, scan the character array from both sides i.e from the start index (left) as well as from last index(right) simultaneously.

   1. Set the left index equal to 0 and right 
      index equal to the length of the string -1.
   2. Swap the characters of the start index 
      scanning with the last index scanning 
      one by one. After that, increase the left 
      index by 1 (left++) and decrease the right 
      by 1 i.e., (right--) to move on to the next 
      characters in the character array .
   3. Continue till left is less than or equal to
      the right.
   

   // Java program to Reverse a String using swapping // of variables import java.lang.*; import java.io.*; import java.util.*;    // Class of ReverseString class ReverseString {     public static void main(String[] args)     {         String input = "Geeks For Geeks";         char[] temparray = input.toCharArray();         int left, right=0;         right = temparray.length-1;            for (left=0; left < right ; left++ ,right--)         {             // Swap values of left and right             char temp = temparray[left];             temparray[left] = temparray[right];             temparray[right]=temp;         }            for (char c : temparray)             System.out.print(c);         System.out.println();     } }

   Output:

   skeeG roF skeeG
   

5. Using ArrayList object: Convert the input string into the character array by using toCharArray() built in method. Then, add the characters of the array into the ArrayList object. Java also has built in reverse() method for the Collections class. Since Collections class reverse() method takes a list object , to reverse the list , we will pass the LinkedList object which is a type of list of characters.

   1. We copy String contents to an object 
      of ArrayList.
   1. We create a ListIterator object by using 
      the listIterator() method on the LinkedList 
      object.
   2. ListIterator object is used to iterate over 
      the list.
   3. ListIterator object helps us to iterate 
      over the reversed list and print it one 
      by one to the output screen.
   

   // Java program to Reverse a String using ListIterator import java.lang.*; import java.io.*; import java.util.*;    // Class of ReverseString class ReverseString {     public static void main(String[] args)     {         String input = "Geeks For Geeks";         char[] hello = input.toCharArray();         List<Character> trial1 = new ArrayList<>();            for (char c: hello)             trial1.add(c);            Collections.reverse(trial1);         ListIterator li = trial1.listIterator();         while (li.hasNext())             System.out.print(li.next());     } }

   Output:

   skeeG roF skeeG
   

Related Article:
Different methods to reverse a string in C/C++

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.