设计模式-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。

装饰模式的优点：

• 装饰模式与继承关系的目的都是要拓展对象的功能，但是装饰模式可以提供比继承更多的灵活性。装饰模式允许系统动态决定“贴上”一个需要的“装饰”，或者“除掉”一个不需要的“装饰”。继承关系则不同，继承关系是静态的，它在系统运行前就决定了。
• 通过不同的具体装饰类以及这些装饰类的排列组合，设计师可以创造出更多不同行为的组合。

装饰模式的缺点：

• 由于使用装饰模式，可以比使用继承关系需要较少数目的类。使用较少的类，当然使设计比较易于进行。但是，在另外一方面，使用装饰模式会产生比使用继承关系所产生的更多的对象。而更多的对象会使得查找错误更为困难，特别是这些对象在看上去极为相似的时候

下面以建筑为例，修饰高层和低层建筑

1.建筑接口

package com.design.demo.decorator;

/**
 * @author: GuanBin
 * @date: Created in 上午12:04 2019/9/9
 */
public interface Building {
    void bulid();
}

2.高层建筑

package com.design.demo.decorator;

/**
 * @author: GuanBin
 * @date: Created in 上午12:05 2019/9/9
 */
public class HighBuilding implements Building {
    @Override
    public void bulid() {
        System.out.println("build high building");
    }
}

3.低层建筑

package com.design.demo.decorator;

/**
 * @author: GuanBin
 * @date: Created in 上午12:06 2019/9/9
 */
public class Cottage implements Building {

    @Override
    public void bulid() {
        System.out.println("bulid cottage");
    }
}

4. 抽象装饰类

package com.design.demo.decorator;

/**
 * @author: GuanBin
 * @date: Created in 上午12:07 2019/9/9
 *
 * //装饰类
 */
public abstract class BuildDecorator implements Building {
    protected Building building;

    public BuildDecorator(Building building) {
        this.building = building;
    }

    @Override
    public void bulid() {
        building.bulid();
    }
}

5.高层和低层的抽象装饰类

package com.design.demo.decorator;

/**
 * @author: GuanBin
 * @date: Created in 上午12:11 2019/9/9
 */
public class HighestDecorator extends BuildDecorator {
    public HighestDecorator(Building building) {
        super(building);
    }

    @Override
    public void bulid() {
        building.bulid();
        System.out.println("It is highest building");
    }
}

package com.design.demo.decorator;

/**
 * @author: GuanBin
 * @date: Created in 上午12:11 2019/9/9
 */
public class LowestDecorator extends BuildDecorator {
    public LowestDecorator(Building building) {
        super(building);
    }

    @Override
    public void bulid() {
        building.bulid();
        System.out.println("It is lowest building");
    }
}

6.测试类

package com.design.demo.decorator;

/**
 * @author: GuanBin
 * @date: Created in 上午12:14 2019/9/9
 */
public class DecoratorPatternDemo {
    public static void main(String[] args) {
        //高层建筑的修饰类
        BuildDecorator highDecorator = new HighestDecorator(new HighBuilding());
        //低层建筑的修饰类
        BuildDecorator lowDecorator = new LowestDecorator(new Cottage());

        highDecorator.bulid();

        lowDecorator.bulid();
    }
}

7.输出

build high building
It is highest building
bulid cottage
It is lowest building

Process finished with exit code 0