java - java中使用System.exit(0)退出程序

Question

我对如何实现 System.exit(0); 有点困惑在我的程序中。我想要发生的是用户输入“exit”一词并让程序终止。我还希望程序在输入“clear”时返回“0.0”，但我认为我在处理变量时遇到问题，因为 num1 和 num2 是 double ，但我希望“exit”和“clear”是可接受的输入，也是如此。

如果有人有任何见解，我们将不胜感激。这是我的代码:

package projectapcs;

/**
 *
 * @author Apple
 */

import java.util.Scanner;

public class ProjectAPCS {

    public static void exit(int x){

    }

    public static void clear(int y){

    }

    public static void main(String[] args) {



    double num1;
    double num2;
    char char1;
    String operation;


    Scanner input = new Scanner(System.in);

    System.out.println 
    ("Enter 'exit' to quit the calculator, 'help' for more options or 'continue' to use the   calculator");


    System.out.println
    ("\nEnter the first number:");
    num1 = input.nextInt();



     System.out.println 
     ("Display:" +  num1);

     System.out.println("Please enter operation:");
    operation = input.next();



    System.out.println("Enter the second number:");
    num2 = input.nextInt();
    System.out.println ("Display:" + num2);





    if ("+".equals(operation)){

        System.out.println((num1 + num2));
    } 
    else if ("-".equals(operation)){ 

        System.out.println((num1 - num2));
    }
    else if ("/".equals(operation)){ 

        System.out.println((num1 / num2));
    }
    else if ("*".equals(operation)){ 

        System.out.println((num1 * num2));
    }
    else if ("-x".equals(operation)){

        System.out.println (-num1);
    }
    else if ("x^2".equals(operation)){

        System.out.println (num1 * num1);
    }
    else if ("sqrt".equals(operation)){

        System.out.println (Math.sqrt(num1));

    }


    else if ("H".equals(num1)){

       System.out.println("Type + for the addition of values");
       System.out.println("Type - for the substraction of values");
       System.out.println("Type * for the multiplcation of values");
       System.out.println("Type / for the division of values");
       System.out.println("Type negate for the negation of values");
       System.out.println("Type ^2 for squaring of values");
    } 

    else if("E".equals(num1)){

       System.out.println ("Calculator program terminated...");
       System.exit(0);
    }

  }

}

Answer 1

如果您想允许任意输入，请将输入读取为字符串，然后 convert to double根据需要:

String input = scanner.next();
if (input.equals("exit")) {
    exit();
else if (input.equals("clear")) {
    clear();
} else {
    try {
        double number = Double.parseDouble(input);
        /* do something with `number` */
    } catch (NumberFormatException e) {
        System.err.println("Not a double.");
    }
}