Java String with only digit by regular expression

import java.util.regex.Pattern;

public class Main {
    public static void main(String[] argv) throws Exception {
        String str = "";
        System.out.println(isNumeric(str));
    }/*from  w ww .ja  v  a 2s.c  om*/

    public static boolean isNumeric(String str) {
        Pattern pattern = Pattern.compile("[0-9]*");
        return pattern.matcher(str).matches();
    }
}