设计模式之装饰器模式

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

文章来源: chenyu.blog.csdn.net，作者：chen.yu，版权归原作者所有，如需转载，请联系作者。

原文链接：chenyu.blog.csdn.net/article/details/103286559