07 桥接模式（Bridge Design Pattern）

一句话概括：把Color抽象出来并作为Shape的一个属性，在Shape初始化的时候确定它是值。

将抽象部分与它的实现部分分离，使他们都可以独立变化。

桥接模式将继承关系转化成关联关系，它降低了类与类之间的耦合度，减少了系统中类的数量，也减少了代码量。

public interface Color{
    void applyColor();
}

public abstract class Shape{

    //桥接
    //Composition - implementor
    protected Color color;

    //constructor with implementor as input argument
    public Shape(Color c){
        this.color = c;
    }

    abstract public void applyColor();
}

The implementation of Shape

public class Triangle extends Shape{
    public Triangle(Color c){
        super(c);
    }

    @Override
    public void applyColor(){
        System.out.print("Triangle filled with color ");
        this.color.applyColor();
    }
}
public class Pentagon extends Shape{

    public Pentagon(Color c) {
        super(c);
    }

    @Override
    public void applyColor() {
        System.out.print("Pentagon filled with color ");
        color.applyColor();
    }

}

The implementation of Color

public class RedColor implements Color{

    public void applyColor(){
        System.out.println("red");
    }
}

public class GreenColor implements Color{
    public void applyColor(){
        System.out.println("green");
    }
}

Lets test our bridge pattern implementation with a test program

public class BridgePatternTest{
    public static void main(String[] args){
        Shape tri = new Triangle(new RedColor());
        tri.applyColor();

        Shape pent = new Pentagon(new GreenClor());
        tri.applyColor();
    }
}

The output of above bridge pattern test progran.

Triangle filled with color red.
Pentagon filled with color green.