Java Program to find Reverse of a String

In Java, to find a reverse of a string is a common task. We can reverse a string with various methods available, such as using loops like while and for, or using StringBuilder for efficiency. For instance, reversing the String “hi” results in “ih”.

In this article we will learn how to find reverse of a String through example, detailed logic and program explanation for better understanding.

Table of Contents

Required Knowledge
Problem Statement
- Example:
Logic to find reverse of a string
Java program to find the reverse of a string
Conclusion

Required Knowledge

Java programming basics
Java operators
StringBuilder
Loop concepts

Problem Statement

We have to write a java program to find the reverse of a string. The program will take input string and should output reverse of the string. This action will be done in our program. Let’s see an example,

Example:

For a given input String str “Learn java through Interview Expert”, Output should be ” trepxE weivretnI hguorht avaj nraeL”.

Explanation:

Input String str: "Learn java through Interview Expert"

The reversed string should start from the last word and each word should be reversed individually.

Reverse of str:  trepxE weivretnI hguorht avaj nraeL

Hence, we have the reverse of the string (str).

Logic to find reverse of a string

There are multiple logics to find a reverse of a string in java programming language.

Logic 1: Using StringBuilder

Take input from string (str) from the user.
Create a StringBuilder object s initialized with the contents of str. The StringBuilder class is used because it provides a convenient method reverse() to reverse the sequence of characters in the string.
After reversing, using print statement display the reversed string.

Logic 2: Using while loop

Take input string (str) from the user.
Convert the string str into a character array ch.
Initialize an empty string revStr to store the reversed string.
Initialize an integer i to the index of the last character in ch.
Using a while loop, iterate from the last character to the first character (i from ch.length-1 to 0).
Inside the loop, append each character from ch to the string revStr in reverse order.
After loop completes, print the string revStr, which now contains the reversed version of the input string str.

Logic 3: Using for loop

Take user input for a text string (str).
Initialize an empty string outputRev to store the reversed string.
Use a for loop to iterate backwards through the characters of str starting from the last character (str.length()-1) down to the first (0).
Inside the loop, append each character (str.charAt(i)) to the outputRev string.
After the loop completes, outputRev contains the reversed string.
Print outputRev to display the reversed string to the user.

Java program to find the reverse of a string

Program 1: Using StringBuilder

In the below program we are using StringBuilder to find the reverse of a string.

import java.util.Scanner;
public class ReverseString {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		System.out.println("Please enter a text");
		String str = sc.nextLine();
		StringBuilder s = new StringBuilder(str);
    s.reverse();
    System.out.println("Reverse of a String: "+ s.toString());        
		sc.close();
	}
}

Output:

Please enter a text
Hi, This is a great learning platform
Reverse of a String: mroftalp gninrael taerg a si sihT ,iH

Java program explanation to find the reverse of a string

The program imports the Scanner class from java.util package to read input from the user.
It defines a class named ReverseString.
Inside the class, there’s a main method, which serves as the entry point of the program.
In the main method:
- It creates a Scanner object named sc to read input from the console.
- Asks the user to enter a text and reads the input using nextLine() method, storing it in the variable str.
- Program creates a StringBuilder object s initialized with the content of the str.
- It calls the reverse() method on the StringBuilder object s to reverse the characters.
- It prints the reversed string using toString() method of StringBuilder.
- Finally, it closes the Scanner object to release system resources.

Program 2 : Using while loop

In the below program we are using while loop to find the reverse of a string in Java.

import java.util.Scanner;
public class ReverseString {
	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		System.out.println("Enter the text :");
		String str = s.nextLine();
		char ch[]= str.toCharArray();    
    String revStr="";
    int i=ch.length-1;
    while(i>=0) {
      revStr+=ch[i];
      i--;
    }
    System.out.println(revStr);
		s.close();
	}
}

Output:

Enter the text :
mroftalp gninrael taerg a si sihT ,iH
Hi, This is a great learning platform

Java program explanation to find the reverse of a string

The program imports the Scanner class from java.util package to read input from the user.
It defines a class named ReverseString.
Inside the class, there’s a main method, which serves as the entry point of the program.
In the main method:
- It creates a Scanner object named s to read input from the console.
- It asks the user to enter a text and reads the input using nextLine() method, storing it in the variable str.
- Then, it converts the string str into a character array ch[] using the toCharArray() method.
- It initializes an empty string revStr to store the reversed text.
- Initializes an integer i to the index of the last character in the array.
- It enters a while loop that iterates from the last character of the array to the first character.
- Inside the loop, it appends each character of the array in reverse order to the revStr string.
- After the loop completes, it prints the revStr string, which contains the reversed text.
- Finally, it closes the Scanner object to release system resources.

Program 3: Using for loop

In the below program we are using while loop to find the reverse of a string.

import java.util.Scanner;
public class ReverseString {
	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		System.out.println("Enter the text :");
		String str = s.nextLine();
    String outputRev="";
    for(int i=str.length()-1;i>=0;i--) {
      outputRev+=str.charAt(i);
    }
    System.out.println(outputRev);
		s.close();
	}
}

Output:

Enter the text :
I Love Interview Expert Website
etisbeW trepxE weivretnI evoL I

Java program explanation to find the reverse of a string

The program imports the Scanner class from java.util package to read input from the user.
It defines a class named ReverseString.
Inside the class, there’s a main method, which serves as the entry point of the program.
In the main method:
- It creates a Scanner object named s to read input from the console.
- Asks the user to enter a text and reads the input using nextLine() method, storing it in the variable str.
- It initializes an empty string outputRev to store the reversed text.
- It enters a for loop that iterates over each character of the string text in reverse order.
- Inside the loop, it appends each character of the string in reverse order to the outputRev string.
- After the loop completes, it prints the outputRev string, which contains the reversed text.
- Finally, it closes the Scanner object to release system resources.

Conclusion

In this article, we have learnt how to find reverse of a string in Java. We have seen the logic and implemented the program using StringBuilder, while loop and for loop in Java. Hope this article helped you in the understanding of the program.

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Happy Java learning!!