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Decorator Pattern in Design Pattern

装饰器模式

Overview

装饰器模式(Decorator Pattern)允许向一个现有的对象添加新的功能,同时又不改变其结构。

这种类型的设计模式属于结构型模式,它是作为现有的类的一个包装。

这种模式创建了一个装饰类,用来包装原有的类,并在保持类方法签名完整性的前提下,提供了额外的功能。

主要解决

一般的,我们为了扩展一个类经常使用继承方式实现,由于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。

何时使用

在不想增加很多子类的情况下扩展类。

应用实例

  • 给画,添加上画框

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模式,装饰模式可以动态扩展一个实现类的功能。

实现

Decorator Pattern

Shape

Shape Interface

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package individual.cy.learn.pattern.structural.decorator;

/**
* @author mystic
*/
public interface Shape {
/**
* to draw a geometric shape
*/
void draw();
}

Circle

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package individual.cy.learn.pattern.structural.decorator;

/**
* @author mystic
*/
public class Circle implements Shape {
@Override
public void draw() {
System.out.println("Circle.draw");
}
}

Rectangle

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package individual.cy.learn.pattern.structural.decorator;

/**
* @author mystic
*/
public class Rectangle implements Shape {
@Override
public void draw() {
System.out.println("Rectangle.draw");
}
}

Decorator

AbstractShapeDecorator

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package individual.cy.learn.pattern.structural.decorator;

/**
* @author mystic
*/
public abstract class AbstractShapeDecorator implements Shape {
protected Shape decoratedShape;

public AbstractShapeDecorator(Shape decoratedShape) {
this.decoratedShape = decoratedShape;
}

@Override
public void draw() {
decoratedShape.draw();
}
}

RedShapeDecorator

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package individual.cy.learn.pattern.structural.decorator;

/**
* @author mystic
*/
public class RedShapeDecorator extends AbstractShapeDecorator {
public RedShapeDecorator(Shape decoratedShape) {
super(decoratedShape);
}

@Override
public void draw() {
super.draw();
setRedBorder(decoratedShape);
}

private void setRedBorder(Shape decoratedShape) {
System.out.println("RedShapeDecorator.setRedBorder");
}
}

VioletShapeDecorator

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package individual.cy.learn.pattern.structural.decorator;

/**
* @author mystic
*/
public class VioletShapeDecorator extends AbstractShapeDecorator {
public VioletShapeDecorator(Shape decoratedShape) {
super(decoratedShape);
}

@Override
public void draw() {
super.draw();
setVioletBorder(decoratedShape);
}

public void setVioletBorder(Shape decoratedShape) {
System.out.println("VioletShapeDecorator.setVioletBorder");
}
}

Tester

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package individual.cy.learn.pattern.structural.decorator;

/**
* @author mystic
*/
public class DecoratorPatternTester {
public static void main(String[] args) {
Shape circle = new Circle();
Shape redCircle = new RedShapeDecorator(new Circle());
Shape redRectangle = new RedShapeDecorator(new Rectangle());
Shape violetCircle = new VioletShapeDecorator(new Circle());
Shape violetRectangle = new VioletShapeDecorator(new Rectangle());
// Shape redCircle = new RedShapeDecorator(Circle::new);
// Shape redRectangle = new RedShapeDecorator(Rectangle::new);
// Shape violetCircle = new VioletShapeDecorator(Circle::new);
// Shape violetRectangle = new VioletShapeDecorator(Rectangle::new);
circle.draw();
redCircle.draw();
redRectangle.draw();
violetCircle.draw();
violetRectangle.draw();
}
}

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Circle.draw
Circle.draw
RedShapeDecorator.setRedBorder
Rectangle.draw
RedShapeDecorator.setRedBorder
Circle.draw
VioletShapeDecorator.setVioletBorder
Rectangle.draw
VioletShapeDecorator.setVioletBorder

如果执行注释的代码,即使用::new创建对象,则输出

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Circle.draw
RedShapeDecorator.setRedBorder
RedShapeDecorator.setRedBorder
VioletShapeDecorator.setVioletBorder
VioletShapeDecorator.setVioletBorder