main方法之args参数

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);
        }        
    }
}