装饰者模式定义：动态地给一个对象增加一些额外的职责，就增加对象功能来说，装饰模式比生成子类实现更为灵活。装饰模式是一种对象结构型模式。
1.新建food接口

package com.zheng.nie.decorator;
/**
 * @author: niezheng1
 * @Date: 2018/12/26 18:13
 */
public interface Food {
   Float cost();
}

构建装饰类实现Food接口，确保装饰者和被装饰者是同一类型。

/**
 * @author: niezheng1
 * @Date: 2018/12/26 18:16
 * 构件装饰类：抽象装饰类
 */
public class Decorator implements Food {

   private Food food;

    public Decorator(Food food) {
        this.food = food;
    }

    @Override
    public Float cost() {
      return food.cost();
    }
}

给煎饼果子加一个培根，继承抽象装饰类

package com.zheng.nie.decorator;

/**
 * @author: niezheng1
 * @Date: 2018/12/26 18:17
 */
public class Bacon extends Decorator {

    public Bacon(Food food) {
        super(food);
    }

    /**
     * 增加培根花费
     * @return
     */
    @Override
    public Float cost() {
      return super.cost()+1.5f;
    }
}

热狗装饰类

package com.zheng.nie.decorator;

/**
 * @author: niezheng1
 * @Date: 2018/12/26 18:23
 */
public class Hotdog extends Decorator{
    public Hotdog(Food food) {
        super(food);
    }


    /**
     * 增加热狗花费
     * @return
     */
    @Override
    public Float cost() {
        return super.cost()+2f;
    }
}

生菜装饰类

package com.zheng.nie.decorator;

/**
 * @author: niezheng1
 * @Date: 2018/12/26 18:25
 */
public class Lettuce extends Decorator {

    public Lettuce(Food food) {
        super(food);
    }

    /**
     * 增加生菜花费
     * @return
     */
    @Override
    public Float cost() {
        return super.cost()+0.5f;
    }
}

新建一个煎饼果子类，实现Food接口。

package com.zheng.nie.decorator;

/**
 * @author: niezheng1
 * @Date: 2018/12/26 18:15
 * 煎饼果子
 */
public class PancakeFruit implements Food{
    @Override
    public Float cost() {
        return 1f;
    }
}

package com.zheng.nie.decorator;

/**
 * @author: niezheng1
 * @Date: 2018/12/26 18:25
 */
public class App {

    public static void main(String[] args) {
        Food food = new PancakeFruit();
        /**用培根装饰**/
        food = new Bacon(food);
        /**加热狗**/
        food = new Hotdog(food);
        /**加生菜*/
        food = new Lettuce(food);
        System.out.println(food.cost());
    }

}

输出如果：

5.0

类图如下

image.png