Easy Way To Reverse String in Java

Introduction

Reversing a string is a common programming task that helps in understanding basic string manipulation techniques. In this task, the order of characters in a given string is reversed. For example, if the input string is “hello”, the output will be “olleh”. This operation can be performed using various methods in Java, such as using a loop, recursion, or built-in functions.

Java Program to Reverse a String

Below is a Java program that reverses a string using a loop:

public class ReverseString {
    public static void main(String[] args) {
        String input = "hello";
        String reversed = reverseString(input);
        System.out.println("Original String: " + input);
        System.out.println("Reversed String: " + reversed);
    }

    public static String reverseString(String str) {
        StringBuilder reversed = new StringBuilder();
        for (int i = str.length() - 1; i >= 0; i--) {
            reversed.append(str.charAt(i));
        }
        return reversed.toString();
    }
}

How the Code Runs

1. Main Method: The main method is the entry point of the program. It defines a string input with the value “hello”.
2. Reverse Method: The reverseString method is called, passing the input string as an argument. This method is responsible for reversing the string.
3. StringBuilder: Inside the reverseString method, a StringBuilder object named reversed is created to hold the reversed string.
4. Looping: A for loop iterates over the string in reverse order, starting from the last character (index str.length() - 1) to the first character (index 0). For each character, it appends the character to the StringBuilder object.
5. Returning the Result: After the loop finishes, the StringBuilder is converted to a string using toString() and returned to the calling method.
6. Output: Finally, the program prints the original string and the reversed string.

Explanation of Steps

Returning the Result: After constructing the reversed string, the StringBuilder is converted back to a String and returned.

StringBuilder: StringBuilder is used to efficiently append characters to the string. It’s mutable, meaning it can change its content without creating a new object each time, which is more efficient than using a regular string in a loop.

Looping: The loop starts from the last character of the string and iterates backward. str.charAt(i) is used to fetch each character at index i.

Appending Characters: Each character obtained from the loop is appended to the StringBuilder object using the append() method.

How the Output is Produced

1. Original String: The string "hello" is assigned to the variable input.
2. Reversed String: The reverseString method reverses the input string by iterating over it from the last character to the first and appending each character to a StringBuilder. The reversed string "olleh" is then returned and stored in the reversed variable.
3. Printing: The program prints the original string and the reversed string to the console.

The output confirms that the program successfully reversed the input string "hello" to "olleh".

Output

Original String: hello
Reversed String: olleh

Conclusion

Reversing a string is a fundamental operation that helps in understanding string manipulation and control flow in Java. This program demonstrates how to reverse a string using a simple loop and StringBuilder, which are effective and efficient tools in Java for such operations. Understanding this basic concept lays the groundwork for tackling more complex string operations and algorithms in future programming tasks.

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