键入＆＃34; quit＆＃34;时不会退出Java循环。

Question

你好，当我输入String＆＃34; quit＆＃34;时，我似乎无法使用while循环来终止代码。任何帮助将不胜感激。

package CalculatorProg;

import java.util.Scanner;

public class MainDriver {

    public static void main(String[] args){

        BinaryExpression operation = new BinaryExpression();

        @SuppressWarnings("resource")
        Scanner userinput = new Scanner(System.in); 


        while(true){


            String calc;
            String num1;
            String num2;

            num1 = userinput.next();
            calc = userinput.next();
            num2 = userinput.next();

            String[] input = new String[5];
            input[0] = num1;
            input[1] = " ";
            input[2] = calc;
            input[3] = " ";
            input[4] = num2;


            if(calc.equals("+")){
                System.out.print(num1);
                System.out.print(" ");
                System.out.print(calc);
                System.out.print(" ");
                System.out.print(num2);
                System.out.print(" ");
                System.out.print("=");
                System.out.print(" ");
                int x, y;
                x = Integer.parseInt(num1);
                y = Integer.parseInt(num2);

                System.out.println(operation.Add(x, y));
            }    
            else if(calc.equals("-")){
                System.out.print(num1);
                System.out.print(" ");
                System.out.print(calc);
                System.out.print(" ");
                System.out.print(num2);
                System.out.print(" ");
                System.out.print("=");
                System.out.print(" ");
                int x, y;
                x = Integer.parseInt(num1);
                y = Integer.parseInt(num2);
                System.out.println(operation.Subtract(x, y));
            }   
            else if(calc.equals("*")){
                System.out.print(num1);
                System.out.print(" ");
                System.out.print(calc);
                System.out.print(" ");
                System.out.print(num2);
                System.out.print(" ");
                System.out.print("=");
                System.out.print(" ");
                int x, y;
                x = Integer.parseInt(num1);
                y = Integer.parseInt(num2);
                System.out.println(operation.Multiply(x, y));
            }   
            else if(calc.equals("/")){
                System.out.print(num1);
                System.out.print(" ");
                System.out.print(calc);
                System.out.print(" ");
                System.out.print(num2);
                System.out.print(" ");
                System.out.print("=");
                System.out.print(" ");
                int x, y;
                x = Integer.parseInt(num1);
                y = Integer.parseInt(num2);
                System.out.println(operation.Divide(x, y));
            }
            else{
                System.out.println("The operation is not valid.");
                }
            if(input[0].equalsIgnoreCase("quit")){
                   break;
            }
        }
        System.exit(0);
    }
}

Answer 1

代码在calc = userinput.next（）;

上等待用户输入

public boolean hasNext（） 如果此扫描器的输入中有另一个标记，则返回true。在等待输入扫描时，此方法可能会阻塞。扫描仪不会超过任何输入。

Answer 2

首先应该在自己的条件下验证输入。

示例：

package CalculatorProg;

import java.util.Scanner;

public class MainDriver {

    public static void main(String[] args) {

        BinaryExpression operation = new BinaryExpression();

        @SuppressWarnings("resource")
        Scanner userinput = new Scanner(System.in);


        while (true) {


            String calc;
            String num1;
            String num2;

            num1 = userinput.next();
            calc = userinput.next();
            num2 = userinput.next();

            String[] input = new String[5];
            input[0] = num1;
            input[1] = " ";
            input[2] = calc;
            input[3] = " ";
            input[4] = num2;

            if (!input[0].equalsIgnoreCase("quit")) {
                if (calc.equals("+")) {
                    System.out.print(num1);
                    System.out.print(" ");
                    System.out.print(calc);
                    System.out.print(" ");
                    System.out.print(num2);
                    System.out.print(" ");
                    System.out.print("=");
                    System.out.print(" ");
                    int x, y;
                    x = Integer.parseInt(num1);
                    y = Integer.parseInt(num2);

                    System.out.println(operation.Add(x, y));
                } else if (calc.equals("-")) {
                    System.out.print(num1);
                    System.out.print(" ");
                    System.out.print(calc);
                    System.out.print(" ");
                    System.out.print(num2);
                    System.out.print(" ");
                    System.out.print("=");
                    System.out.print(" ");
                    int x, y;
                    x = Integer.parseInt(num1);
                    y = Integer.parseInt(num2);
                    System.out.println(operation.Subtract(x, y));
                } else if (calc.equals("*")) {
                    System.out.print(num1);
                    System.out.print(" ");
                    System.out.print(calc);
                    System.out.print(" ");
                    System.out.print(num2);
                    System.out.print(" ");
                    System.out.print("=");
                    System.out.print(" ");
                    int x, y;
                    x = Integer.parseInt(num1);
                    y = Integer.parseInt(num2);
                    System.out.println(operation.Multiply(x, y));
                } else if (calc.equals("/")) {
                    System.out.print(num1);
                    System.out.print(" ");
                    System.out.print(calc);
                    System.out.print(" ");
                    System.out.print(num2);
                    System.out.print(" ");
                    System.out.print("=");
                    System.out.print(" ");
                    int x, y;
                    x = Integer.parseInt(num1);
                    y = Integer.parseInt(num2);
                    System.out.println(operation.Divide(x, y));
                } else {
                    System.out.println("The operation is not valid.");
                }
            } else {
                break;
            }
        }
        System.exit(0);
    }
}

Answer 3

尝试检查＆＃39;退出＆＃39;在任何其他条件之前：

package CalculatorProg;

import java.util.Scanner;

public class MainDriver {

    public static void main(String[] args){

        BinaryExpression operation = new BinaryExpression();

        @SuppressWarnings("resource")
        Scanner userinput = new Scanner(System.in); 


        while(true){


            String calc;
            String num1;
            String num2;

            num1 = userinput.next();
            if(num1.equalsIgnoreCase("quit")){
                   break;
            }
            calc = userinput.next();
            num2 = userinput.next();

            String[] input = new String[5];
            input[0] = num1;
            input[1] = " ";
            input[2] = calc;
            input[3] = " ";
            input[4] = num2;



            if(calc.equals("+")){
                System.out.print(num1);
                System.out.print(" ");
                System.out.print(calc);
                System.out.print(" ");
                System.out.print(num2);
                System.out.print(" ");
                System.out.print("=");
                System.out.print(" ");
                int x, y;
                x = Integer.parseInt(num1);
                y = Integer.parseInt(num2);

                System.out.println(operation.Add(x, y));
            }    
            else if(calc.equals("-")){
                System.out.print(num1);
                System.out.print(" ");
                System.out.print(calc);
                System.out.print(" ");
                System.out.print(num2);
                System.out.print(" ");
                System.out.print("=");
                System.out.print(" ");
                int x, y;
                x = Integer.parseInt(num1);
                y = Integer.parseInt(num2);
                System.out.println(operation.Subtract(x, y));
            }   
            else if(calc.equals("*")){
                System.out.print(num1);
                System.out.print(" ");
                System.out.print(calc);
                System.out.print(" ");
                System.out.print(num2);
                System.out.print(" ");
                System.out.print("=");
                System.out.print(" ");
                int x, y;
                x = Integer.parseInt(num1);
                y = Integer.parseInt(num2);
                System.out.println(operation.Multiply(x, y));
            }   
            else if(calc.equals("/")){
                System.out.print(num1);
                System.out.print(" ");
                System.out.print(calc);
                System.out.print(" ");
                System.out.print(num2);
                System.out.print(" ");
                System.out.print("=");
                System.out.print(" ");
                int x, y;
                x = Integer.parseInt(num1);
                y = Integer.parseInt(num2);
                System.out.println(operation.Divide(x, y));
            }
            else{
                System.out.println("The operation is not valid.");
                }
        }
        System.exit(0);
    }
}

问题可能在于它正试图解析“退出”问题。到整数，这会导致错误并且永远不会达到退出条件。

或者可能是代码正在等待输入＆＃39; calc = userinput.next（）;＆＃39;，但我不确定您是否尝试输入下两个输入< / p>

Answer 4

代码可能会停留在第二个next()来电。只需拨打一次nextLine()电话，然后拨打String::split

即可

String input = userinput.nextLine(); // Get an entire line

if (input.equalsIgnoreCase("quit")){ // Check the exit first
    break;
}
// If it hasn't exited assume that its an equation

String[] inputSplit = input.split(); // Split the input by spaces
String calc inputSplit[1];
String num1 inputSplit[0];
String num2 inputSplit[2];

Answer 5

我希望它适合你。在程序运行时，我会向用户提供一些帮助信息。你可以尝试一下！ ：d

package CalculatorProg;

import java.util.Scanner;

public class MainDriver {

public static void main(String[] args){

    BinaryExpression operation = new BinaryExpression();

    @SuppressWarnings("resource")
    Scanner userinput = new Scanner(System.in); 


    while(true){


        String calc;
        String num1;
        String num2;

        System.out.print("Number 1 (if quit then program exits) =");
        num1 = userinput.next();
        if(num1.equalsIgnoreCase("quit")) {
            System.out.println("program quit");
            break;
        }
        System.out.print("Operator =");
        calc = userinput.next();
        System.out.print("Number 2 =");
        num2 = userinput.next();

        String[] input = new String[5];
        input[0] = num1;
        input[1] = " ";
        input[2] = calc;
        input[3] = " ";
        input[4] = num2;


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

            int x, y;
            x = Integer.parseInt(num1);
            y = Integer.parseInt(num2);
            System.out.println(num1 + " " + calc + " " + num2 + " " + "=" + " " + operation.Add(x,y));
            //System.out.println(num1 + " " + calc + " " + num2 + " " + "=" + " " + (x+y));
        }    
        else if(calc.equals("-")){
            int x, y;
            x = Integer.parseInt(num1);
            y = Integer.parseInt(num2);
            System.out.println(num1 + " " + calc + " " + num2 + " " + "=" + " " + operation.Subtract(x, y));
            //System.out.println(num1 + " " + calc + " " + num2 + " " + "=" + " " + (x-y));
        }   
        else if(calc.equals("*")){
            int x, y;
            x = Integer.parseInt(num1);
            y = Integer.parseInt(num2);
            System.out.println(num1 + " " + calc + " " + num2 + " " + "=" + " " + operation.Multiply(x, y));
            //System.out.println(num1 + " " + calc + " " + num2 + " " + "=" + " " + (x*y));
        }   
        else if(calc.equals("/")){
            int x, y;
            x = Integer.parseInt(num1);
            y = Integer.parseInt(num2);
            System.out.println(num1 + " " + calc + " " + num2 + " " + "=" + " " + operation.Divide(x, y));
            //System.out.println(num1 + " " + calc + " " + num2 + " " + "=" + " " + (x/y));
        }
        else{
            System.out.println("The operation is not valid. You can give +, -, *, / for operator!");
            }
    }
    System.exit(0);
}

}