java - 子类如何在双胞胎设计模式中进行交流？

Question

我正在研究 Twin 设计模式。我理解了这个概念，但是当涉及到实现时，我无法完全理解子类之间是如何通信的。

子类如何交流或交换消息？

Example image of twin design pattern structure

Answer 1

两个子类能够相互通信，因为它们都构成了彼此的对象。

让我们以 Wikipedia article "Twin pattern" 中的以下示例为例理解这一点:

public class BallItem extends GameItem {
     BallThread twin;

     int radius; int dx, dy;
     boolean suspended;

     public void draw(){
        board.getGraphics().drawOval(posX-radius, posY-radius,2*radius,2*radius);
     }

     public void move() { 
       posX += dx; posY += dy; 
     }

     public void click() {
       if (suspended) twin.resume(); else twin.suspend();
       suspended = ! suspended;
     }

     public boolean intersects (GameItem other) {
      if (other instanceof Wall)
       return posX - radius <= other.posX && other.posX <= posX + radius || posY - radius <= other.posY && other.posY <= posY + radius;

      else return false;
     }

     public void collideWith (GameItem other) {
      Wall wall = (Wall) other;
      if (wall.isVertical) dx = - dx; else dy = - dy;
     }
}

public class BallThread extends Thread {
   BallItem twin;
   public void run() {
     while (true) {
       twin.draw(); /*erase*/ twin.move(); twin.draw();
     } 
   }
}

假设 BallThread 想要扩展 Thread 和 BallItem。但是你看，BallThread继承了Thread，组成了一个BallItem类。通过引用 BallItem 类(或组合 BallItem 类)，BallThread 将能够调用 BallItem 类的所有方法。

Hence, BallThread is achieving Multiple Inheritance by inheriting Thread class and composing BallItem class.