设计模式学习笔记--装饰器模式

十、装饰器模式

装饰器模式(Decorator Pattern)允许向一个现有的对象添加新的功能，同时不改变其结构。
通过创建一个装饰类，包装原有的类，保持原有类的方法签名不变，提供额外功能。

介绍

动态的给一个对象添加一些额外的新功能，相比生成子类更为灵活。
相比使用继承，装饰模式避免了由继承而引入的静态特征和子类臃肿的现象。
- 优点：装饰类和被装饰类可以独立发展，不会相互耦合，装饰模式是继承的一个替代方式，可以动态扩展一个现有类的功能。
- 缺点：多层装饰比较复杂。

实现

创建一个Shape接口和实现该接口的实体类，然后欻功能键一个实现Shape接口的装饰类ShapeDecorator
并把Shape对象作为它的实例变量。RedShapeDecorator实现ShapeDecorator的实体类，完成功能扩展。

- 创建接口

Shape.java

public interface Shape {  void draw();}

• 创建接口实现类

Rectangle.java

public class Rectangle implements Shape {  @override  public void draw(){    System.out.println("Shape : Rectangle");  }}

Circle.java

public class Circle implements Shape {  @override  public void draw(){    System.out.println("Shape : Circle");  }}

• 创建抽象的装饰类

ShapeDecorator.java

public abstract class ShapeDecorator implements Shape{  protected Shape decorateShape;  public ShapeDecorator(Shape decorateShape){    this.decorateShape = decorateShape;  }  public void draw(){    decorateShape.draw();  }}

• 创建实体的装饰类

RedShapeDecorator.java

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");  }}

• 演示

DecoratorPatternDemo.java

public class DecoratorPatternDemo {  public static void main(String[] args){    Shape circle = new Circle();    Shape redCircle = new RedShapeDecorator(new Circle());    Shape redRectangle = new RedShapeDecorator(new Rectangle());    System.out.println("Circle with normal border");    circle.draw();    System.out.println("\n Circle of red border");    redCircle.draw();    System.out.println("\n Rectangle of red border");    redRectangle.draw();  }}

• 输出

Circle with normal borderShape: CircleCircle of red borderShape: CircleBorder Color: RedRectangle of red borderShape: RectangleBorder Color: Red