java - 当我运行 switch case 并选择一个选项时，它将不断循环该选项

Question

我的目标是要求用户输入一个操作，它将从另一个进行基本计算的类中进行计算，然后它将获取结果，并要求用户再次选择一个操作，并继续相同的操作数字。或者选择C并将数字清0

import java.util.Scanner;

public class CalculatorClient {

    public static void main(String[] args) {
        Scanner keyboard = new Scanner(System.in);

        System.out.println("Welcome to calculator\n You will be able to use this program to add, subtract, multiply, and divide values!\n");
        double number1;
        System.out.println("Enter a number: ");
        number1 = keyboard.nextDouble();
        Calculator obj1 = new Calculator(number1);
        keyboard.nextLine();

        // System.out.println("Please enter an operation ( + , - , / , *) :");
        // input=keyboard.nextLine();

        System.out.println("Please enter an operation ( + , - , / , *) :");
        String input = keyboard.nextLine();;

我不知道为什么，但我用来测试运算符(operator)输入的 while 循环在运行时不起作用。

        while  (!"+".equals(input) || !"-".equals(input) || !"/".equals(input) || !"*".equals(input)) {
                System.out.println("That is not a valid operation, please enter an operation ( + , - , / , *) :");
                input = keyboard.nextLine();
        }    



        int counter=0;    
        Loopy:
        while(counter<1)

        {
            switch (input) {
                case "+": {
                    int add;
                    System.out.println("Enter a second number to add: ");
                    add = keyboard.nextInt();
                    System.out.println("\nThe sum is: ");
                    System.out.println("The nubmer is now ");
                    System.out.println(obj1.getNumber());
                    System.out.println(obj1.add(add));
                    number1 = obj1.getNumber();
                    break;
                }   
                case "-": {
                    int subtract;
                    System.out.println("Enter a second number to subtract: ");
                    subtract = keyboard.nextInt();
                    System.out.println("\nThe difference is: ");
                    System.out.println(obj1.subtract(subtract));
                    System.out.println("The nubmer is now ");
                    System.out.println(obj1.getNumber());
                    number1 = obj1.getNumber();
                    break;
                }
                case "/": {
                    int div;
                    System.out.println("Enter a second number to divide");
                    div = keyboard.nextInt();
                    System.out.println("\nThe quotient is: ");
                    System.out.println(obj1.divide(div));
                    System.out.println("The nubmer is now ");
                    System.out.println(obj1.getNumber());
                    number1 = obj1.getNumber();
                    break;
                }
                case "*": {
                    int times;
                    System.out.println("Enter a second nubmer to multiply");
                    times = keyboard.nextInt();
                    System.out.println("\nThe product is: ");
                    System.out.println("The nubmer is now ");
                    System.out.println(obj1.getNumber());
                    System.out.println(obj1.multiply(times));
                    number1 = obj1.getNumber();
                    break;
                }
                case "C": {
                    obj1.setNumber(number1);
                    System.out.println("The nubmer is now ");
                    System.out.println(obj1.getNumber());
                    break;

                }
            }

        counter--;

由于某种原因，这个 println 最终打印了两次

        System.out.println("\nPlease enter an operation ( + , - , / , *) :");
        input = keyboard.nextLine();
        continue;
        }
    }
}

````

Here is my calculator program (My instruction is to make it on a separate file
````
public class Calculator
{
    private double number;

    Calculator(double x){number=x;}
    Calculator(){}

    public void setNumber(double x){number=x;}
    public double getNumber(){return number;}



            public double add(double a){
                number+=a;
                return (number);
            } 
            public double subtract(double a){
                number-=a;
                return (number);
            }

            public double multiply(double a){
                number*=a;
                return (number);
            }

            public double divide(double a){
                number/=a;
                return (number);
            }
}

Answer 1

我认为您的问题在以下几行中:int计数器=0;
循环: while(计数器<1)** 你的方法逻辑**最后——反--；

因此计数器始终小于 1，因此始终处于循环中