java: cannot find a symbol when trying to use .isDigit()

Question

Tried both in my IDE and in the online IDE my textbook on Zybooks.com gives me to work in. My goal is to check whether or not the variable passCode contains a digit. Here's the code:

public class CheckingPasscodes{
    public static void main (String [] args) {
        boolean hasDigit = false;
        String passCode = "";
        int valid = 0;

        passCode = "abc";

        if (passCode.isDigit(passCode.charAt(0)) || passCode.isDigit(passCode.charAt(1)) || passCode.isDigit(passCode.charAt(2))) {
            hasDigit = true;
        }

        if (hasDigit) {
            System.out.println("Has a digit.");
        }
        else {
            System.out.println("Has no digit.");
        }
    }
}

I get the error on line 9 (where the first if starts):

java: cannot find symbol
symbol: method isDigit(char)
location: variable passCode of type java.lang.String

Tried changing passCode.charAt(0) (or 1 and 2) to simply 'a' (or 'b' and 'c') to test whether it was because I was putting a method inside another method, but I seem to get the same error.

I eventually solved the problem by asking a friend, who provided me this, instead:

char s = passCode.charAt(0);
char s1 = passCode.charAt(1);
char s2 = passCode.charAt(2);

if ((s>'0' && s<'9') || (s1>'0' && s1<'9') || (s2>'0' && s2<'9')) {
    hasDigit=true;
}

It makes perfect sense, and I did think of doing something similar, but the chapter in which this exercise is isn't about .charAt()—we covered that before—but rather about .isDigit() and other character operations, so doing what I did is all but cheating.

This is driving me nuts.

P.S.: I'm pretty new to Java, so, if the answer is something really obvious, I'm really sorry. And thanks for taking your time to read all this!

Answer 1

You're calling .isDigit() on a String object, which doesn't have such a method. It's a static method of the Character class.

Character.isDigit(passCode.charAt(0));

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A big hint is that your error message stated the following:

location: variable passCode of type java.lang.String

which should automatically prompt you to look at the String class for the documentation on whatever method you're looking for - and, subsequently, to discover it doesn't have such a method.