桥接模式

桥接模式

桥接模式是软件设计模式中最复杂的模式之一，它把事物对象和其具体行为、具体特征分离开来，使它们可以各自独立的变化。事物对象仅是一个抽象的概念。如“圆形”、“三角形”归于抽象的“形状”之下，而“画圆”、“画三角”归于实现行为的“画图”类之下，然后由“形状”调用“画图”。

结构

Abstraction

定义抽象的接口

该接口包含实现具体行为、具体特征的Implementor接口

Refined Abstraction

抽象接口Abstraction的子类，依旧是一个抽象的事物名

Implementor

定义具体行为、具体特征的应用接口

ConcreteImplementor

实现Implementor接口

示例

下列各语言的代码都用于写出两个不同的圆的坐标和半径。

API1.circle at 1:2 7.5
API2.circle at 5:7 27.5

Java

/** "Implementor" */
interface DrawingAPI
{
    public void drawCircle(double x, double y, double radius);
}
 
/** "ConcreteImplementor" 1/2 */
class DrawingAPI1 implements DrawingAPI
{
   public void drawCircle(double x, double y, double radius) 
   {
        System.out.printf("API1.circle at %f:%f radius %f\n", x, y, radius);
   }
}
 
/** "ConcreteImplementor" 2/2 */
class DrawingAPI2 implements DrawingAPI
{
   public void drawCircle(double x, double y, double radius) 
   { 
        System.out.printf("API2.circle at %f:%f radius %f\n", x, y, radius);
   }
}
 
/** "Abstraction" */
interface Shape
{
   public void draw();                                            // low-level
   public void resizeByPercentage(double pct);     // high-level
}
 
/** "Refined Abstraction" */
class CircleShape implements Shape
{
   private double x, y, radius;
   private DrawingAPI drawingAPI;
   public CircleShape(double x, double y, double radius, DrawingAPI drawingAPI)
   {
       this.x = x;  this.y = y;  this.radius = radius; 
       this.drawingAPI = drawingAPI;
   }
 
   // low-level i.e. Implementation specific
   public void draw()
   {
        drawingAPI.drawCircle(x, y, radius);
   }   
   // high-level i.e. Abstraction specific
   public void resizeByPercentage(double pct)
   {
        radius *= pct;
   }
}
 
/** "Client" */
class BridgePattern {
   public static void main(String[] args)
   {
       Shape[] shapes = new Shape[2];
       shapes[0] = new CircleShape(1, 2, 3, new DrawingAPI1());
       shapes[1] = new CircleShape(5, 7, 11, new DrawingAPI2());
 
       for (Shape shape : shapes)
       {
           shape.resizeByPercentage(2.5);
           shape.draw();
       }
   }
}