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Can anyone tell me the solution of this problem?

write an expression to detect that the first character of userinput matches firstletter.

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Have you tried following

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, charAt(0) and substring(0, 1) will throw a StringIndexOutOfBoundsExceptionstartsWith does not have this problem.

To make the entire condition one line and avoid length checks, you can alter the regexes to the following:

// or the equivalent

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.

Hope it helps

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