怎么判断一个字符是数字

// 如何判断一个字符是数字public class Test{    /* 测试函数 */    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.用JAVA自带的函数 */    private static boolean isDigitA(char ch)    {        return Character.isDigit(ch);    }    /* 2.用正则表达式 */    private static boolean isDigitB(char ch)    {        Pattern pattern = Pattern.compile("[0-9]");        return pattern.matcher(String.valueOf(ch)).matches();    }    /* 3.用ascii码 */    private static boolean isDigitC(char ch)    {        if (ch < 48 || ch > 57)            return false;        else            return true;    }    /* 4.强制类型转化是否抛出异常来判断 */    private static boolean isDigitD(char ch)    {        try        {            int i = Integer.parseInt(String.valueOf(ch));            return true;        }        catch (NumberFormatException e)        {            e.printStackTrace();            return false;        }    }}