Java中具有翻转参数的调用方法

Question

I have a few subclasses of Shape:

Rectangle, Circle, etc.

I also have a methods in each class like this:

class Rectangle extends Shape{
    public void isIntersecting(Circle circle){ ... }  
}

class Circle extends Shape{
    public void isIntersecting(Rectangle rectangle){ ... }  
}

These methods obviously would be repeated code. My question is, how do I avoid something like this?

Answer 1

The simple answer is to implement (for instance) Circle's intersection method as:

public void isIntersecting(Rectangle rectangle) {
    rectangle.isIntersecting(this);
}

I can't think of a more elegant method.

---

The problem with defining the API method as this:

public void isIntersecting(Shape) { ... }

is that you end up having to code an "instanceof" switch with a case for each of the different shapes. The repetitious code is still there, and you've replaced the static typing with something that is potentially more fragile ...

(AFAIK, there is no general / efficient algorithm for testing if two arbitrary shapes intersect. Especially if the shapes involve curved lines.)

Answer 2

You could implement them once (in either class or as a static method somewhere) and have all methods call that shared code.

class Rectangle extends Shape{
   public boolean isIntersecting(Circle circle){ 
      return Shapes.isIntersecting(this, circle);
   }  
} 

class Circle extends Shape{
   public boolean isIntersecting(Rectangle rectangle){
       return Shapes.isIntersecting(rectangle, this);
   }  
}

class Shapes{
    static boolean isIntersecting(Rectangle rectangle, Circle circle){
       // implementation goes here
    }
}