Bridge Pattern

Bridge Pattern

桥接模式，引用“四人帮的话”就是 “decouple an abstraction from its implementation so that the two can vary independently”，抽象与行为分离。

说个例子

客户想画图，画两种圆和矩形，每种矩形都要调用特别的划线（draw_a_line()）方法，每一种圆也是。如果像上面那样，是不是感觉混乱了点？看看下面的呢。

这个是不是舒服点？的确，图形和画法都存在一一对应的关系，我们完全可以把图形这个抽象和画法这个行为分离，而不需要一个画法对应多个抽象，如上面那个。

public   abstract   class  Shape
{
    public abstract void draw();
}

// 画点和圆的方法
public   abstract   class  ShapeDrawing
{
    public abstract void draw_a_line();
    public abstract void draw_a_circle();
}

public   class  ShapeDrawingSingleton
{
    private static ShapeDrawing shapedrawingSingleton;
    
    public ShapeDrawingSingleton(ShapeDrawing shapedrawing)
    {
        shapedrawingSingleton=shapedrawing;
    }
    
    public static ShapeDrawing getShapeDrawing()
    {
        return shapedrawingSingleton;
    }
}

// 画图方法基类
public   class  VShape  extends  Shape
{
    public ShapeDrawing shapedrawing;
    
    public void setShapeDrawing()
    {
        this.shapedrawing=ShapeDrawingSingleton.getShapeDrawing();
    }
    
    public ShapeDrawing getShapeDrawing()
    {
        return this.shapedrawing;
    }
}

public   class  V1Circle  extends  VShape
{
    public Circle(){setShapeDrawing();}
    
    public void draw()
    {
        //用shapedrawing画圆
        //shapedrawing.draw_a_circle()
    }
}

//
// V1Rectangle和V2系列参照上面的
//

public   class  DP1ShapeDrawing  extends  ShapeDrawing
{
    public void draw_a_line(){};
    public void draw_a_circle(){};
}

public   class  DP2ShapeDrawing  extends  ShapeDrawing
{
    public void draw_a_line(){};
    public void draw_a_circle(){};
}

ShapeDrawingSingleton shapedrawingSingleton = new  ShapeDrawingSingleton( new  DP1ShapeDrawing());

V1Circle v1circle = new  V1Circle();
v1circle.draw();

// 其他的类似于上面的

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