如何调用 java 主函数

Question

public class Calculator {
    public static void main(String[] args) {
        if (args.length < 3) {
            System.out.println("Usage: java Calculator operand1 operator operand2");
            System.exit(0);
        }
        int result = 0;
        switch (args[1].charAt(0)) {
        case '+':
            result = Integer.parseInt(args[0]) + Integer.parseInt(args[1]);
            break;
        case '-':
            result = Integer.parseInt(args[0]) - Integer.parseInt(args[1]);
            break;
        case '*':
            result = Integer.parseInt(args[0]) * Integer.parseInt(args[1]);
            break;
        case '/':
            result = Integer.parseInt(args[0]) / Integer.parseInt(args[1]);
            break;
        }
        System.out.println(args[0] + ' ' + args[1] + ' ' + args[2] + " = " + result);
    }
}

当我在终端中运行Calculator.java时，我尝试了以下几种方法：

Rasperry:src maggiesmac$ javac Calculator.java
Rasperry:src maggiesmac$ java Calculator 1+2
Usage: java Calculator operand1 operator operand2
Rasperry:src maggiesmac$ java Calculator 1 + 2
Exception in thread "main" java.lang.NumberFormatException: For input string: "+"
    at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
    at java.lang.Integer.parseInt(Integer.java:572)
    at java.lang.Integer.parseInt(Integer.java:615)
    at Calculator.main(Calculator.java:15)
Rasperry:src maggiesmac$ java Calculator.main(1,+,2)
-bash: syntax error near unexpected token `('

那么如何调用 Java main() 方法呢？我应该如何将参数传递给它？

Answer 1

请更改案例结构中的索引(如 @SotiriosDelimanolis 所示(。此外，我们可以在以下情况下使用字符串：

public class Calculator {
    public static void main(String[] args) {
        if (args.length < 3) {
            System.out.println("Usage: java Calculator operand1 operator operand2");
            System.exit(0);
        }
        int result = 0;
        switch (args[1]) {
        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);
    }
}

Answer 2

你也可以试试下面的代码得到结果

class Calculator {
    public static void main(String[] args) {
        if (args.length < 3) {
            System.out.println("Usage: java Calculator operand1 operator operand2");
            System.exit(0);
        }
        int result = 0;
    char op = args[1].charAt(0);
    System.out.println((int)op);
    int ope = (int)op;
        switch (ope) {
        case 43:
            result = Integer.parseInt(args[0]) + Integer.parseInt(args[2]);
            break;
        case 45:
            result = Integer.parseInt(args[0]) - Integer.parseInt(args[2]);
            break;
        case 42:
            result = Integer.parseInt(args[0]) * Integer.parseInt(args[2]);
            break;
        case 47:
            result = Integer.parseInt(args[0]) / Integer.parseInt(args[2]);
            break;
        }
        System.out.println(args[0] + ' ' + args[1] + ' ' + args[2] + " = " + result);
    }
}