In Java is there a way to find out if first character of a string is a number?
One way is
and do the above all the way till 9, but that seems very inefficient.
Note that this will allow any Unicode digit, not just 0-9. You might prefer:
char c = string.charAt(0); isDigit = (c >= '0' && c <= '9');
Or the slower regex solutions:
s.substring(0, 1).matches("\d") // or the equivalent s.substring(0, 1).matches("[0-9]")
However, with any of these methods, you must first be sure that the string isn’t empty. If it is,
substring(0, 1) will throw a
startsWith does not have this problem.
To make the entire condition one line and avoid length checks, you can alter the regexes to the following:
s.matches("\d.*") // or the equivalent s.matches("[0-9].*")
If the condition does not appear in a tight loop in your program, the small performance hit for using regular expressions is not likely to be noticeable.