Introduction to Java Programming编程题12.1<NumberFormatException>

运行结果：

br:javacode br$ javac NumberFormatException.java
br:javacode br$ java NumberFormatException 45 34
Please use java NumberFormatException operand1 operator operand2
java NumberFormatException 45x + 34
Wrong input 45x
java NumberFormatException 45 1 33
Wrong input: 1
java NumberFormatException 45 / 3
45 / 3 = 15.0

NumberFormatException.java (不使用异常处理)

class NumberFormatException {
    public static void main(String[] args) {
        if (args.length != 3) {
            System.out.println("Please use java NumberFormatException operand1 operator operand2");
            System.exit(1);
        }

        if (isDigital(args[0])) {
            if (args[1].length() == 1) {
                if (args[1].charAt(0) == '+' || args[1].charAt(0) == '-'
                        || args[1].charAt(0) == '*' || args[1].charAt(0) == '/') {
                    if (isDigital(args[2])) {
                        char operator = args[1].charAt(0);
                        double result = 0;
                        switch (operator) {
                            case '+':
                                result = Integer.parseInt(args[0]) + Integer.parseInt(args[2]);
                                break;
                            case '-':
                                result = Integer.parseInt(args[0]) - Integer.parseInt(args[2]);
                                break;
                            case '*':
                                result = Integer.parseInt(args[0]) * Integer.parseInt(args[2]);
                                break;
                            case '/':
                                result = Integer.parseInt(args[0]) / Integer.parseInt(args[2]);
                                break;
                        }
                        System.out.println(args[0] + ' ' + args[1] + ' ' + args[2] + " = " + result);
                        System.exit(0);
                    }
                } else
                    System.out.println("Wrong input: " + args[1]);
            } else
                System.out.println("Wrong input: " + args[1]);
        }

        System.exit(1);
    }

    public static boolean isDigital(String args) {
        for (int i = 0; i < args.length(); i++)
            if (!Character.isDigit(args.charAt(i))) {
                System.out.println("Wrong input " + args);
                return false;
            }

        return true;
    }


}

NumberFormatException1.java (使用异常处理)

class NumberFormatException1 {
    public static void main(String[] args) {

      try {
        if (args.length != 3)
            throw new IllegalArgumentException ("Please use java NumberFormatExceptionX operand1 operator operand2");

        if (isDigital(args[0])) {
            if (args[1].length() == 1) {
                if (args[1].charAt(0) == '+' || args[1].charAt(0) == '-'
                        || args[1].charAt(0) == '*' || args[1].charAt(0) == '/') {
                    if (isDigital(args[2])) {
                        char operator = args[1].charAt(0);
                        double result = 0;
                        switch (operator) {
                            case '+':
                                result = Integer.parseInt(args[0]) + Integer.parseInt(args[2]);
                                break;
                            case '-':
                                result = Integer.parseInt(args[0]) - Integer.parseInt(args[2]);
                                break;
                            case '*':
                                result = Integer.parseInt(args[0]) * Integer.parseInt(args[2]);
                                break;
                            case '/':
                                result = Integer.parseInt(args[0]) / Integer.parseInt(args[2]);
                                break;
                        }
                        System.out.println(args[0] + ' ' + args[1] + ' ' + args[2] + " = " + result);
                    }
                }
            }
        }
      }
      catch (IllegalArgumentException e) {
        System.out.println(e);
      }

    }

    public static boolean isDigital(String args) {
        for (int i = 0; i < args.length(); i++)
            if (!Character.isDigit(args.charAt(i)))
                return false;

        return true;
    }


}