Example: PalindromeCheckRecursive in Java

// PalindromeCheckRecursive
import java.util.Scanner;

public class Main {

    // Helper method to preprocess the string
    private static String preprocessString(String s) {
        StringBuilder cleanedString = new StringBuilder();
        for (char c : s.toCharArray()) {
            if (Character.isLetterOrDigit(c)) {
                cleanedString.append(Character.toLowerCase(c));
            }
        }
        return cleanedString.toString();
    }

    // Method to check for palindrome using recursion
    public static boolean isPalindromeRecursive(String s) {
        String cleaned = preprocessString(s);
        return checkRecursive(cleaned, 0, cleaned.length() - 1);
    }

    private static boolean checkRecursive(String s, int left, int right) {
        // Base Case 1: If left pointer crosses or meets right pointer, it's a palindrome
        if (left >= right) {
            return true;
        }

        // Base Case 2: If characters at current pointers don't match
        if (s.charAt(left) != s.charAt(right)) {
            return false;
        }

        // Recursive Step: Check the inner substring
        return checkRecursive(s, left + 1, right - 1);
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // Step 1: Get input string from the user
        System.out.print("Enter a string to check for palindrome: ");
        String inputString = scanner.nextLine();

        // Step 2: Check if it's a palindrome using the recursive method
        if (isPalindromeRecursive(inputString)) {
            System.out.println("'" + inputString + "' is a palindrome (Recursive Method).");
        } else {
            System.out.println("'" + inputString + "' is NOT a palindrome (Recursive Method).");
        }

        scanner.close();
    }
}