Verify if String is hexadecimal

Question

I have a String like "09a" and I need a method to confirm if the text is hexadecimal. The code I've posted does something similar, it verifies that a string is a decimal number. I want to do the same, but for hexadecimal.

    private static boolean isNumeric(String cadena) {
    try {
        Long.parseLong(cadena);
        return true;
    } catch (NumberFormatException nfe) {
        JOptionPane.showMessageDialog(null,"Uno de los números, excede su capacidad.");
        return false;
    }
}

Answer 1

There's an overloaded Long.parseLong that accepts a second parameter, specifying the radix:

Long.parseLong(cadena,16); 

As an alternative, you could iterate over the characters in the string and call Character.digit(c,16) on them (if any of them return -1 it's not a valid hexadecimal digit). This is especially useful if the string is too large to fit in a long (as pointed out in the comments, that would cause an exception if the first method is used). Example:

private static boolean isNumeric(String cadena) {     if ( cadena.length() == 0 ||           (cadena.charAt(0) != '-' && Character.digit(cadena.charAt(0), 16) == -1))         return false;     if ( cadena.length() == 1 && cadena.charAt(0) == '-' )         return false;      for ( int i = 1 ; i < cadena.length() ; i++ )         if ( Character.digit(cadena.charAt(i), 16) == -1 )             return false;     return true; } 

BTW, I'd suggest separating the concerns of "testing for a valid number" and "displaying a message to the user", that's why I simply returned false in the example above instead of notifying the user first.

Finally, you could simply use a regular expression:

cadena.matches("-?[0-9a-fA-F]+"); 

Answer 2

Horrible abuse of exceptions. Don't ever do this! (It's not me, it's Josh Bloch's Effective Java). Anyway, I suggest

private static final Pattern HEXADECIMAL_PATTERN = Pattern.compile("\\p{XDigit}+");

private boolean isHexadecimal(String input) {
    final Matcher matcher = HEXADECIMAL_PATTERN.matcher(input);
    return matcher.matches();
}