Hexadecimal to Decimal Number

/* Using loops write a program that converts a hexadecimal integer number to its decimal form.
 * The input is entered as string. The output should be a variable of type long. */

import java.util.Scanner;

public class _15_HexadecimalToDecimalNumber {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner scan = new Scanner(System.in);
        System.out.print("Enter your Hexadecimal number on the line: ");
        String hexadecStr = scan.next();
        scan.close();

        if (hexadecStr.indexOf("0x") <= 0) {
            if (hexadecStr.indexOf("0x") == 0) {
                hexadecStr = hexadecStr.substring(2);
            }

            hexadecStr = hexadecStr.toUpperCase();

            // Short variant:
            // long decNum = Long.parseLong(hexadecStr, 16);

            long decNum = 0;
            long multiplier = 1;
            for (int i = hexadecStr.length() - 1; i >= 0; i--) {
                char hexDigit = hexadecStr.charAt(i);
                int tempNum = convertHexadecimalCharToDecimalNumber(hexDigit);
                decNum += tempNum * multiplier;
                multiplier *= 16;
            }

            System.out.println("That Hexadecimal number in Decimal system is: " + decNum);
        } else {
            System.out.println("Error! - Invalid Input number!!!");
        }
    }

    private static int convertHexadecimalCharToDecimalNumber(char digit) {
        // TODO Auto-generated method stub
        switch (digit) {
        case 'A':
            return 10;
        case 'B':
            return 11;
        case 'C':
            return 12;
        case 'D':
            return 13;
        case 'E':
            return 14;
        case 'F':
            return 15;

        default:
            return Integer.parseInt("" + digit);
        }
    }

}