java - 由于某种原因，Switch 语句与情况 8 不同。编译器表现得很奇怪

Question

这是代码:

public static void main(String args[])
    {
        int i=0;
        int m=0;
        double scale;
        boolean exit;
        Shape[] s = new Shape[10];
        while(exit !=true)
        {
            System.out.print("\nChoose an option:\n"+
                    "1-Add a new circle\n"+
                    "2-Add a new rectangle\n"+
                    "3-Delete all shapes\n"+
                    "4-Scale all shapes\n"+
                    "5-Display perimeter of all shapes\n"+
                    "6-Display the area of all shapes\n"+
                    "7-Enter scale factor\n"+
                    "8-Exit program\n");

            Scanner input = new Scanner(System.in);
            m=input.nextInt();


            if(i<=9)
            {
                switch (m)
                {


                 case 1: Circle c = new Circle(0);
                         s[i]=c;
                         i++;
                         break;
                 case 2: Rectangle r = new Rectangle(1,1);
                         s[i]=r;
                         i++;
                         break;

                 case 3: s=null;
                         i=0;
                         break;
                 case 4: for(i=0; i<s.length; i++)
                         {
                             s[i].scaleShape();
                         }
                         break;
                 case 5: for(i=0; i<s.length; i++)
                         {
                            if(s[i] != null)
                            {   
                                System.out.println(s[i].getPerimeter());
                            }
                         }
                         break;
                 case 6: for(i=0; i<s.length; i++)
                         {
                            if(s[i] != null)
                            {
                                System.out.println(s[i].getArea());
                            }
                         }
                         break;
                 case 7: do
                         {
                            System.out.println("\nEnter scale factor");
                            scale=input.nextDouble();
                         }
                         while(scale<0);
                         Shape.setScaleFactor(scale);

                         }
                         break;

                 case 8: System.out.println("Do you want to quit?");
                         break; //Nothing here since loop should terminate it.



                 //default: System.out.println("Number must be 1-8");
                         // break;


              } 

         }
     }
   }

奇怪的是，编译器在第 8 种情况下给了我一个错误:

Type mismatch can't convert from int to boolean.

但我没有将任何内容转换为 boolean 值

-syntax error on token "case" assert expected -syntax error on token :, ; expected

但是那里的所有命令都有分号

expression must return a value

为什么编译器的行为如此有趣？通常这样的错误很容易发现。这是怎么回事？

Answer 1

您的问题是在 7 的情况下:

case 7: do
        {
             System.out.println("\nEnter scale factor");
             scale=input.nextDouble();
        }
        while(scale<0);
        Shape.setScaleFactor(scale);

        }

请注意额外的右大括号:它会关闭您的 switch 语句，从而孤立您的 case 8。