是什么？

场景案例：想必大家都吃过手抓饼吧，我们在点手抓饼的时候可以选择加培根、鸡蛋、火腿、肉松等等这些配菜，当然这些配菜的价格都不一样，那么计算总价就比较麻烦；

装饰者模式就是指在不改变现有对象结构的情况下，动态地给该对象增加一些职责（即额外功能）；

结构

抽象构件：定义一个抽象接口以规范准备接收附加责任的对象；

具体构件：实现抽象构件，通过装饰角色为其添加一些职责；

抽象装饰：继承或实现抽象构件，并包含具体构件的实例，可以通过其子类扩展具体构件的功能；

具体装饰：实现抽象装饰的相关方法，并给具体构件对象添加附加的责任；

实现

通过继承

抽象构件

public abstract class HandGraspStore {
    //手抓饼店铺==>抽象构建
    private float price;
    private String desc;

    public HandGraspStore() {

    }

    public HandGraspStore(float price, String desc) {
        this.price = price;
        this.desc = desc;
    }

    public Float getPrice() {
        return price;
    }

    public void setPrice(float price) {
        this.price = price;
    }

    public String getDesc() {
        return desc;
    }

    public void setDesc(String desc) {
        this.desc = desc;
    }
    public abstract float cost();
}

具体构件

public class HandGraspCake extends HandGraspStore{
    //手抓饼===>具体构件

    public HandGraspCake() {
        super(10,"手抓饼");
    }

    @Override
    public float cost() {
       return super.getPrice();
    }
}

抽象装饰

public abstract class Decorator extends HandGraspStore {
    //抽象装饰
    private HandGraspStore handGraspStore;

    public HandGraspStore getHandGraspStore() {
        return handGraspStore;
    }

    public void setHandGraspStore(HandGraspStore handGraspStore) {
        this.handGraspStore = handGraspStore;
    }

    public Decorator(HandGraspStore handGraspStore,float price,String desc) {
        super(price,desc);
        this.handGraspStore=handGraspStore;
    }
}

具体装饰

public class Egg extends Decorator{
    //鸡蛋===>具体装饰
    public Egg(HandGraspStore handGraspStore) {
        super(handGraspStore,1,"加一个鸡蛋");
    }

    @Override
    public float cost() {
        return getPrice()+ getHandGraspStore().cost();
    }

    @Override
    public String getDesc() {
        return super.getDesc()+getHandGraspStore().getDesc();
    }
}
public class Ham extends Decorator{
    //培根===>具体装饰
    public Ham(HandGraspStore handGraspStore) {
        super(handGraspStore,3,"加一个火腿");
    }

    @Override
    public float cost() {
        return getPrice()+ getHandGraspStore().cost();
    }

    @Override
    public String getDesc() {
        return super.getDesc()+getHandGraspStore().getDesc();
    }
}

用户使用

public class Customer {
    public static void main(String[] args) {
        HandGraspCake handGraspCake = new HandGraspCake();
        System.out.println(handGraspCake.getDesc()+handGraspCake.getPrice()+"元");
        System.out.println("==============================");
        Egg egg = new Egg(handGraspCake);
        System.out.println(egg.getDesc()+egg.cost()+"元");
        System.out.println("===============================");
        Ham ham = new Ham(egg);
        System.out.println(ham.getDesc()+ham.cost()+"元");
    }
}

通过接口

抽象构件

public interface IHandGraspCakeStore {
    float price();
    String desc();
    float cost();
}

具体构件

public class IHandGraspStore implements IHandGraspCakeStore {
    @Override
    public float price() {
        return 10;
    }

    @Override
    public String desc() {
        return "手抓饼";
    }

    @Override
    public float cost() {
        return price();
    }
}

抽象装饰

public interface IDecoratorStore extends IHandGraspCakeStore {

}

具体装饰

public class IEggStore implements IDecoratorStore {

    private IHandGraspCakeStore handGraspCake;

    public IEggStore(IHandGraspCakeStore handGraspCake) {
        this.handGraspCake=handGraspCake;
    }



    @Override
    public float price() {
        return 1;
    }

    @Override
    public String desc() {
        return handGraspCake.desc()+"加鸡蛋";
    }

    @Override
    public float cost() {
        return price()+ handGraspCake.cost();
    }
}

用户使用

public class ICustomerDemo {
    public static void main(String[] args) {
        IHandGraspStore iHandGrasp = new IHandGraspStore();
        System.out.println(iHandGrasp.desc()+iHandGrasp.cost()+"元");
        System.out.println("================================");
        IEggStore iEgg = new IEggStore(iHandGrasp);
        System.out.println(iEgg.desc()+iEgg.cost()+"元");
        IEggStore eg = new IEggStore(iEgg);
        System.out.println(eg.desc()+eg.cost()+"元");
    }
}