输入 "quit"时 Java 循环未退出

Question

您好，当我输入字符串“quit”时，我似乎无法让 while 循环终止代码。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

代码正在等待用户输入 calc = userinput.next();

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