装饰器模式

单一职责原则：就一个类而言，应该仅有一个引起它变化的原因。

核心

把一个类中的核心职责和装饰功能分开，被装饰对象当做参数传入装饰者对象。动态地给一个对象添加一些额外的职责。

好处

装饰类和被装饰类可以独立发展，不会相互耦合，把类中的装饰功能从类中搬除，简化原有的类，去除相关类中的重复装饰的逻辑。

例子

情景：本类是形状，用颜色装饰类装饰。其中，我们将把一个形状装饰上不同的颜色，同时又不改变形状类。

//创建一个接口public interface Shape{  void draw();}//创造实体类Circle实现接口public class Circle implements Shape {  public void draw(){        System.out.println("Shape: Circle");    }}//创建实现接口的实体类Rectanglepublic class Rectangle implements Shape {  public void draw(){        System.out.println("Shape: Rectangle");    }}//创建实现了 Shape 接口的抽象装饰类。public abstract class ShapeDecorator implements Shape {  protected Shape decoratedShape;    public ShapeDecorator(Shape decoratedShape){        this.decoratedShape = decoratedShape;    }    public void draw(){        decoratedShape.draw();    }}//创建扩展了 ShapeDecorator 类的实体装饰类。public class RedShapeDecorator extends ShapeDecorator{  public RedShapeDecorator(Shape decoratedShape) {        super(decoratedShape);    }    public void draw(){        decoratedShape.draw();        setRedBorder(decoratedShape);    }    private void setRedBorder(Shape decoratedShape) {        System.out.println("Border Color: Red");    }}//最后是客户端程序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("\nCircle of red border");      redCircle.draw();      System.out.println("\nRectangle of red border");      redRectangle.draw();   }}//程序输出Circle with normal borderShape: CircleCircle of red borderShape: CircleBorder Color: RedRectangle of red borderShape: RectangleBorder Color: Red

例子来源http://www.runoob.com/design-pattern/decorator-pattern.html

源码在我的代码托管上
装饰者模式