How to Reverse a String in Java Without Using Inbuilt Functions – Step-by-Step Guide

Create a Program to Reverse a String Without Using Inbuilt Methods in Java

Reversing a string is one of the most common problems asked in beginner-level coding interviews. While Java offers built-in functions like StringBuilder.reverse() or array methods to make this task easier, understanding how to reverse a string manually without using any inbuilt methods is important to strengthen your logic-building skills.

In this tutorial, we will write a Java program that reverses a string without using any built-in methods, and we’ll explain each step in simple terms.

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📌 Problem Statement

Write a Java program to reverse a string manually (without using StringBuilder, StringBuffer, Collections, or any other inbuilt reverse functions).

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💡 Approach

To reverse a string manually:

1. Read the string input from the user.

2. Convert the string into a character array.

3. Use a loop to traverse the array from the end to the beginning.

4. Construct the reversed string by appending characters in reverse order.

5. Display the reversed string.

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✅ Java Code to Reverse a String Without Inbuilt Methods

import java.util.Scanner;

public class ReverseStringManual {
    public static void main(String[] args) {
        // Step 1: Create Scanner object to read input
        Scanner scanner = new Scanner(System.in);

        // Step 2: Ask user to enter a string
        System.out.print("Enter a string to reverse: ");
        String original = scanner.nextLine();

        // Step 3: Convert string to character array
        char[] characters = original.toCharArray();

        // Step 4: Initialize an empty string to store the reversed string
        String reversed = "";

        // Step 5: Loop through the character array in reverse order
        for (int i = characters.length - 1; i >= 0; i--) {
            reversed += characters[i]; // Append each character to 'reversed'
        }

        // Step 6: Print the reversed string
        System.out.println("Reversed String: " + reversed);

        // Close the scanner
        scanner.close();
    }
}

🧠 Step-by-Step Explanation

Let’s break it down line by line so that even beginners can understand:

🔹 Step 1: Import Scanner and Create Main Class

import java.util.Scanner;

We import the Scanner class to read user input.

public class ReverseStringManual {
    public static void main(String[] args) {

We define the main method – the entry point of our Java program.

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🔹 Step 2: Take Input from User

Scanner scanner = new Scanner(System.in);
System.out.print("Enter a string to reverse: ");
String original = scanner.nextLine();

• We create a Scanner object to read input.

• We prompt the user to enter a string.

• The input is stored in a variable named original.

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🔹 Step 3: Convert String to Character Array

char[] characters = original.toCharArray();

• The toCharArray() method converts the string into a character array.

• This lets us access each letter one by one using indexes.

Note: This is just a conversion; we are not using any reverse logic here.

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🔹 Step 4: Initialize an Empty String for the Result

String reversed = "";

• We create an empty string to hold the reversed result.

• We will keep adding characters to this from the end of the original string.

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🔹 Step 5: Loop from End to Start of the Array

for (int i = characters.length - 1; i >= 0; i--) {
    reversed += characters[i];
}

• This loop starts from the last character (length - 1) and ends at the first (i >= 0).

• On each iteration, it appends the character at position i to the reversed string.

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🔹 Step 6: Display the Result

System.out.println("Reversed String: " + reversed);

• We print the reversed string to the console.

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🔹 Step 7: Close the Scanner

scanner.close();

• his is good practice to release the resource used by Scanner.

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📌 Example Output

Input:

Enter a string to reverse: Hello Java

Output:

Reversed String: avaJ olleH

⚠️ Important Notes

• We used basic string and character operations.

• We avoided using StringBuilder, StringBuffer, or any library function that reverses strings directly.

• This method is simple and educational for understanding how strings work internally.

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✅ Time and Space Complexity

• Time Complexity: O(n), where n is the length of the string (we go through each character once).

• Space Complexity: O(n), for storing the reversed string.

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🔚 Conclusion

Reversing a string without inbuilt methods is a great way to build problem-solving skills in Java. This approach teaches how to manipulate strings and arrays manually, which is essential for coding interviews and logic-building exercises.

You can try improving this by:

• Using a char[] to build the result instead of a string (to improve performance).

• Handling null or empty string cases.

• Making it work for multiple strings using functions.