How to determine whether a character is a number

[Java] // how to determine whether a character is a digital public class Test {/* Test function */public static void main (String [] args) {char [] ch = {'A', '1', 'B', '2', 'C', '3', 'D ', '4',}; System. out. println (ch [0] + ":" + isDigitA (ch [0]); System. out. println (ch [1] + ":" + isDigitA (ch [1]); System. out. println (ch [2] + ":" + isDigitB (ch [2]); System. out. println (ch [3] + ":" + isDigitB (ch [3]); System. out. println (ch [4] + ":" + isDigitC (ch [4]); System. out. println (ch [5] + ":" + isDigitC (ch [5]); System. out. println (ch [6] + ":" + isDigitD (ch [6]); System. out. println (ch [7] + ":" + isDigitD (ch [7]);}/* 1. use the built-in function */private static boolean isDigitA (char ch) {return Character. isDigit (ch);}/* 2. use the regular expression */private static boolean isDigitB (char ch) {Pattern pattern = Pattern. compile ("[0-9]"); return pattern. matcher (String. valueOf (ch )). matches ();}/* 3. use the ascii code */private static boolean isDigitC (char ch) {if (ch <48 | ch> 57) return false; else return true;}/* 4. whether to throw an exception to force type conversion to determine */private static boolean isDigitD (char ch) {try {int I = Integer. parseInt (String. valueOf (ch); return true;} catch (NumberFormatException e) {e. printStackTrace (); return false ;}}}