文字が数字であることを判断する方法

//            
public class Test
{
    /*      */
    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. JAVA      */
    private static boolean isDigitA(char ch)
    {
        return Character.isDigit(ch);
    }

    /* 2.       */
    private static boolean isDigitB(char ch)
    {
        Pattern pattern = Pattern.compile("[0-9]");
        return pattern.matcher(String.valueOf(ch)).matches();
    }

    /* 3. ascii  */
    private static boolean isDigitC(char ch)
    {
        if (ch < 48 || ch > 57)
            return false;
        else
            return true;
    }

    /* 4.                */
    private static boolean isDigitD(char ch)
    {
        try
        {
            int i = Integer.parseInt(String.valueOf(ch));
            return true;
        }
        catch (NumberFormatException e)
        {
            e.printStackTrace();
            return false;
        }

    }
}