设计模式：10-装饰器模式

一。适用场景：在一个现有类增加新的功能的场景，基本的思路是用类的聚合代替继承。该模式和桥接模式比较相似。
二。比如，有一个形状(Shape)接口(interface),定义如下：

package cn.edu.tju.app;

public interface Shape {
    void drawIt();
}

其有两个实现类：Rectangle和Circle,

package cn.edu.tju.app;

public class Rectangle implements Shape {
    @Override
    public void drawIt() {
        System.out.println("画长方形");
    }
}

package cn.edu.tju.app;

public class Circle implements Shape {
    @Override
    public void drawIt() {
        System.out.println("画原型");
    }
}

现在，要给形状类增加装饰：画笔颜色，定义一个抽象的装饰器类：

package cn.edu.tju.app;

public class AbstractShapeDecorator implements  Shape{
    Shape shape;

    public Shape getShape() {
        return shape;
    }

    public void setShape(Shape shape) {
        this.shape = shape;
    }


    @Override
    public void drawIt() {
        shape.drawIt();
    }
}

然后，分别定义两个类实现上述的抽象装饰器类，

package cn.edu.tju.app;

public class RedPenShapeDecorator extends AbstractShapeDecorator {
    public RedPenShapeDecorator(Shape shape){
        super.setShape(shape);
    }
    @Override
    public void drawIt(){
        super.drawIt();
        System.out.println("画笔的颜色是红色的");
    }
}

package cn.edu.tju.app;

public class BlackPenShapeDecorator extends AbstractShapeDecorator {
    public BlackPenShapeDecorator(Shape shape){
        super.setShape(shape);
    }
    @Override
    public void drawIt(){
        super.drawIt();
        System.out.println("画笔的颜色是黑色的");
    }
}

最后，在主类中分别调用RedPenShapeDecorator类对象以及BlackPenShapeDecorator类对象的drawIt()方法。

package cn.edu.tju.app;

public class DecoratorTest {
    public static void main(String[] args) {
        AbstractShapeDecorator abstractShapeDecorator1=new BlackPenShapeDecorator(new Rectangle());
        AbstractShapeDecorator abstractShapeDecorator2=new RedPenShapeDecorator(new Circle());
        abstractShapeDecorator1.drawIt();
        abstractShapeDecorator2.drawIt();
    }
}

运行结果如下：