Example: Reverse String Using Recursion in Java

// Reverse String Using Recursion
public class Main {

    /**
     * Recursively reverses the input string.
     *
     * @param str The string to be reversed.
     * @return The reversed string.
     */
    public static String reverseStringRecursive(String str) {
        // Step 1: Define the base case.
        // If the string is empty or has only one character, it's already reversed.
        if (str == null || str.isEmpty() || str.length() == 1) {
            return str;
        }

        // Step 2: Define the recursive step.
        // Call the function for the substring starting from the second character,
        // then concatenate the first character to the end of the result.
        return reverseStringRecursive(str.substring(1)) + str.charAt(0);
    }

    public static void main(String[] args) {
        // Step 3: Test the recursive function with an example string.
        String originalString1 = "hello";
        String reversedString1 = reverseStringRecursive(originalString1);
        System.out.println("Original String: \"" + originalString1 + "\"");
        System.out.println("Reversed String: \"" + reversedString1 + "\"");

        // Test with another string
        String originalString2 = "recursion";
        String reversedString2 = reverseStringRecursive(originalString2);
        System.out.println("\nOriginal String: \"" + originalString2 + "\"");
        System.out.println("Reversed String: \"" + reversedString2 + "\"");

        // Test with an empty string
        String originalString3 = "";
        String reversedString3 = reverseStringRecursive(originalString3);
        System.out.println("\nOriginal String: \"" + originalString3 + "\"");
        System.out.println("Reversed String: \"" + reversedString3 + "\"");

        // Test with a null string
        String originalString4 = null;
        String reversedString4 = reverseStringRecursive(originalString4);
        System.out.println("\nOriginal String: " + originalString4);
        System.out.println("Reversed String: " + reversedString4);
    }
}