Question

Am I misinterpreting something regarding Java regexes? Shouldn’t the following match the leading zero:

public class Testit {
    public static void main(String[] args) {
        format("0115724848");
    }


    private static void format(String elementToFormat) {
        if (elementToFormat.matches("^0")) {
            System.out.println("leading zero:" + elementToFormat);
        } else {
            System.out.println("no leading zero:" + elementToFormat);
        }
    }
}

Answer 1

matches tries to match the pattern against the whole of the input string… and your input string isn’t just “beginning of string followed by 0”.

Either you need "0.*" (the ^ is unnecessary precisely because matches will match the whole string) or you could create a Pattern and then use:

if (pattern.matcher(text).lookingAt())

Of course it’s not clear why you’re using a regex here at all, in that you can use:

if (text.startsWith("0"))