/* 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;
    }

}