1 装饰器模式
装饰器模式允许向一个现有的对象添加新的功能，同时又不改变其结构，它是作为现有类的一个包装。
2 类图实现
这里最关键的是我们装饰器类（抽象类）既实现了原始功能接口（Shape接口）又和原始接口是关联关系（Shape接口作为这个抽象装饰类的成员变量）
3 代码实现
public interface Shape { void draw(); }
public class Rectangle implements Shape { @Override public void draw() { System.out.println("Shape: Rectangle"); } }
public class Circle implements Shape { @Override public void draw() { System.out.println("Shape: Circle"); } }
public abstract class ShapeDecorator implements Shape { protected Shape decoratedShape; public ShapeDecorator(Shape decoratedShape){ this.decoratedShape = decoratedShape; } public void draw(){ decoratedShape.draw(); } }
public class RedShapeDecorator extends ShapeDecorator { public RedShapeDecorator(Shape decoratedShape) { super(decoratedShape); } @Override public void draw() { decoratedShape.draw(); setRedBorder(decoratedShape); } private void setRedBorder(Shape decoratedShape){ System.out.println("Border Color: Red"); } }
public class DecoratorPatternDemo { public static void main(String[] args) { Shape circle = new Circle(); ShapeDecorator redCircle = new RedShapeDecorator(new Circle()); ShapeDecorator redRectangle = new RedShapeDecorator(new Rectangle()); //Shape redCircle = new RedShapeDecorator(new Circle()); //Shape redRectangle = new RedShapeDecorator(new Rectangle()); System.out.println("Circle with normal border"); circle.draw(); System.out.println("\nCircle of red border"); redCircle.draw(); System.out.println("\nRectangle of red border"); redRectangle.draw(); } }
4 运行结果
Circle with normal border Shape: Circle Circle of red border Shape: Circle Border Color: Red Rectangle of red border Shape: Rectangle Border Color: Red
5 优点
1）继承的缺点：如果我们用继承的方式增加新功能，继承为类引入静态特征，并且随着扩展功能的增多，子类会很膨胀
2）装饰器的有点：装饰类和被装饰类可以独立发展，不相互耦合，装饰模式是继承的一个替代模式，装饰模式可以动态扩展一个实现类的功能
部分参考：https://www.runoob.com/design-pattern/decorator-pattern.html
