Problem: Write a Java program to reverse a string, given that the string could be a single word or a sentence.
Example:
1 2 3 4 5 | Input: Pencil Output: licneP Input: Java Program Output: margorP avaJ |
We can reverse a string in Java in multiple ways. Let’s discuss each of the methods in detail.
Reverse String in Java using For Loop
- Input the string (
str). - Loop through the string from back to front (
i). - Concatenate each character at
iofstrtorev. - Output
rev.
Here is the implementation of the steps in Java.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | import java.util.Scanner; public class StringReverse { public static void main(String args[]){ Scanner in =new Scanner(System.in); String str, rev = ""; //Input String System.out.println("Enter a String"); str = in.nextLine(); //Loop from back to front through 'str' for(int i=str.length()-1; >=0; i--){ rev = rev + str.charAt(i); } System.out.println("Reversed String: "+rev); } } |
Note: use nextLine() instead of next() to read the sentence as input.
Output
Enter a String pencil programmer Reversed String: remmargorp licnepReverse String in Java using While Loop
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 | import java.util.Scanner; public class ReverseString { public static void main(String args[]){ Scanner in =new Scanner(System.in); String str, rev = ""; //Input String System.out.println("Enter a String"); str = in.nextLine(); //last index of string int l = str.length()-1; //Loop from back to front through 'str' while(l >= 0){ rev = rev + str.charAt(l--); } System.out.println("Reversed String: "+rev); } } |
Output
Enter a String Reversing a string Reversed String: gnirts a gnisreveRIn this method, we are using the same approach as the first java program but instead of for loop, we are using while loop.
The loop starts from the last index of the input string (i.e str.length()-1) and will end on 0.
Reverse String in Java Without Loop
Java has StringBuilder class has inbuilt reverse() method to reverse a string.
We have to create an instance of StringBuilder using the input string as a parameter.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | import java.util.Scanner; public class ReverseStringWL { public static void main(String args[]){ Scanner in =new Scanner(System.in); String str, rev = ""; //Input String System.out.println("Enter a String"); str = in.nextLine(); StringBuilder sb = new StringBuilder(str); //Rerver using reverse() method rev =sb.reverse().toString(); System.out.println("Reversed String: "+rev); } } |
Output
Enter a String Dhoni Reversed String: inohDIn this tutorial, we learned to reverse a string in Java using loop and without using loop.