Octal to Decimal Conversion Program

import java.util.Scanner;

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

        // Prompt the user to enter an octal number
        System.out.print("Enter an octal number: ");
        String octalNumber = scanner.nextLine();

        // Validate if the input is a valid octal number
        if (!isValidOctal(octalNumber)) {
            System.out.println("Invalid octal number.");
        } else {
            // Convert octal to decimal
            int decimalNumber = octalToDecimal(octalNumber);
            System.out.println("Decimal equivalent: " + decimalNumber);
        }

        scanner.close();
    }

    // Function to check if a string is a valid octal number
    public static boolean isValidOctal(String octal) {
        // A valid octal number consists of digits 0-7
        return octal.matches("^[0-7]+$");
    }

    // Function to convert an octal number to decimal
    public static int octalToDecimal(String octal) {
        int decimalNumber = 0;
        int length = octal.length();

        // Convert each digit from right to left
        for (int i = 0; i < length; i++) {
            char digit = octal.charAt(i);
            int digitValue = digit - '0'; // Convert char to integer

            // Multiply the current decimal number by 8 and add the current digit's value
            decimalNumber = decimalNumber * 8 + digitValue;
        }

        return decimalNumber;
    }
}