public class Demo {

    public static void main (String[] arr) {

        if (arr.length < 3) {

            System.out.println("please input [java] [file] number1 [+-x/] number2");

            System.exit(-1);

        }

        double number1 = Double.parseDouble(arr[0]);

        double number2 = Double.parseDouble(arr[2]);

        if (arr[1].equals("+")) {

            System.out.println(number1 + number2);

        }

        if (arr[1].equals("-")) {

            System.out.println(number1 - number2);

        }

        if (arr[1].equals("x")) {//命令行不可以输入"*"号，因为它有特殊含义，是通配符

            System.out.println(number1 * number2);

        }

        if (arr[1].equals("/")) {

            if (number2 == 0) {

                System.out.println("被除数不能为0");

            }

            System.out.println(number1 / number2);

        }

    }

}