parseInt vs isDigit

Question

I need my code to return true if the parameter is the String representation of an integer between 0 and 255 (including 0 and 255), false otherwise.

For example: Strings "0", "1", "2" .... "254", "255" are valid.

Padded Strings (such as "00000000153") are also valid.

isDigit apparently would also work but i was wondering if this would be more beneficial and/or this would even work with Padded Strings?

public static boolean isValidElement(String token) {
    int foo = Integer.parseInt("token");
    if(foo >= 0 && foo <= 255)
        return true;
    else 
        return false;
    }

Answer 1

isDigit would not work, because it takes a character as input, and returns true if it is a digit from 0 to 9. [Reference : isDigit javadoc]

Since in your case you need to test string representations of all numbers from 0 to 255 hence you must use parseInt.

Additionally also check if the token passed is a valid number by catching NumberFormatException and returning false in case it is not a valid integer.

public static boolean isValidElement(String token) {
    try{
        int foo = Integer.parseInt(token);
        if(foo >= 0 && foo <= 255)
            return true;
        else 
            return false;
    } catch (NumberFormatException ex) {
        return false;
    }
}