设计模式之桥接 Bridge

重点

• 抽象与实现分离

• 解决继承爆炸、用于系统有多个角度分类。（下面的例子，可已根据shape分类，也可以根据draw的颜色分类）不使用桥接模式的情况下，如果有三个角度分类、每个角度有两个分类的话，需要继承实现2^3=8个类，用了桥接模式只需要继承实现2*3=6个类。

  
  桥接

public interface DrawAPI {
   public void draw();
}

public class RedPencil implements DrawAPI {
   @Override
   public void draw() {
      System.out.println("Drawing with Red Pencil");
   }
}

public class GreenPen implements DrawAPI {
   @Override
   public void draw() {
      System.out.println("Drawing with Green Pen");
   }
}

public abstract class Shape {
   protected DrawAPI drawAPI;
   protected Shape(DrawAPI drawAPI){
      this.drawAPI = drawAPI;
   }
   public abstract void draw();  
}

public class Circle extends Shape {
 
   public Circle(DrawAPI drawAPI) {
      super(drawAPI);
   }
 
   public void draw() {
      drawAPI.draw();
   }
}

public class Rectangle extends Shape {
 
   public Rectangle(DrawAPI drawAPI) {
      super(drawAPI);
   }
 
   public void draw() {
      drawAPI.draw();
   }
}

public class BridgePatternDemo {
   public static void main(String[] args) {
      Shape redCircle = new Circle(new RedPencil());
      Shape greenRectangle = new Rectangle(new GreenPen());
 
      RedPencil.draw();
      GreenPen.draw();
   }
}