结构型模式————装饰器模式（3.1）

什么是装饰器模式？

【先吃三颗栗子：】

1.PC=主机+显示器+键盘+鼠标+鼠标垫

主机是核心，而其他的组成部分都是装饰。

2.手抓饼=饼+鸡蛋+培根+黄瓜

饼是核心，鸡蛋，培根是可选的，可以理解为装饰。

3.咖啡=咖啡+牛奶+冰+方糖

咖啡是核心，牛奶等可选。

比喻虽然形象生动，但是与实际或多或少会产生偏差。

抽象的解释：装饰器模式的目的——核心部分和装饰部分可以自由组合。

装饰器模式的功能

对于软件开发来说，聚焦于软件的灵活性和可扩展性。

装饰器模式要求：

• 装饰可选
• 装饰可扩展
• 核心部分可扩展

手抓饼中的装饰器模式

实现饼加各种配料的价格计算。

思路：

1.定义抽象类手抓饼，其中包含获取种类的抽象方法和获取价格的抽象方法。

2.然后定义两个分别为大份手抓饼和中份手抓饼来继承这个抽象类，重写两个方法定义种类和价格。

3.定义具体的配料类继承手抓饼抽象类，先定义构造器传入已经创建的手抓饼种类，然后重写种类和价格方法。

在网上看的一些博客，是创建出一个抽象的配料类来继承抽象产品类，然后用具体的配料类来实现抽象配料类，实现装饰。

可是如果直接将抽象产品类的方法全部定义抽象方法，配料类直接继承重写，实现装饰，功能上也是可以实现的，如下所示，Bacon类直接继承HandPancake，然后重写getName和getCost方法，实现装饰。似乎也没有问题：

但是设计模式毕竟是一种经验总结，如果有已经看出端倪的小伙伴们在下方留言交流一下吧！

直接继承HandPancake：

abstract class HandPancake
{
    public abstract String getName();

    public abstract int getCost();
}

class HandPancake_Big extends HandPancake
{
    @Override
    public String getName() {
        return "大份手抓饼";
    }

    @Override
    public int getCost() {
        return 10;
    }
}

class HandPancake_Mid extends HandPancake
{
    @Override
    public String getName() {
        return "中份手抓饼";
    }

    @Override
    public int getCost() {
        return 8;
    }
}
class Bacon extends HandPancake
{
    private HandPancake handPancake;

    Bacon(HandPancake handPancake)
    {
        this.handPancake=handPancake;
    }

    @Override
    public String getName() {
        return handPancake.getName()+"加培根";
    }

    @Override
    public int getCost() {
        return handPancake.getCost()+1;
    }
}
class Cucumber extends HandPancake
{
    private HandPancake handPancake;

    Cucumber(HandPancake handPancake)
    {
        this.handPancake=handPancake;
    }

    @Override
    public String getName() {
        return handPancake.getName()+"加黄瓜";
    }

    @Override
    public int getCost() {
        return handPancake.getCost()+2;
    }
}
class Ham extends HandPancake
{
    private HandPancake handPancake;

    Ham(HandPancake handPancake)
    {
        this.handPancake=handPancake;
    }

    @Override
    public String getName() {
        return handPancake.getName()+"加火腿";
    }

    @Override
    public int getCost() {
        return handPancake.getCost()+1;
    }
}


public class APPlication
{
    public static void main(String[] args) {
        HandPancake handPancake_big = new HandPancake_Big();

        System.out.println("啥也不加"+handPancake_big.getName()+":"+handPancake_big.getCost());

        handPancake_big = new Ham(handPancake_big);

        System.out.println(handPancake_big.getName()+":"+handPancake_big.getCost());

        handPancake_big = new Cucumber(handPancake_big);

        System.out.println(handPancake_big.getName()+":"+handPancake_big.getCost());

        handPancake_big = new Bacon(handPancake_big);

        System.out.println(handPancake_big.getName()+":"+handPancake_big.getCost());

        System.out.println("==============================");
        HandPancake handPancake_mid = new HandPancake_Mid();
        System.out.println("啥也不加"+handPancake_mid.getName()+":"+handPancake_mid.getCost());

        handPancake_mid = new Ham(handPancake_mid);

        System.out.println(handPancake_mid.getName()+":"+handPancake_mid.getCost());

        handPancake_mid = new Cucumber(handPancake_mid);

        System.out.println(handPancake_mid.getName()+":"+handPancake_mid.getCost());

        handPancake_mid = new Bacon(handPancake_mid);

        System.out.println(handPancake_mid.getName()+":"+handPancake_mid.getCost());


    }
}

官方做法：

abstract class HandPancake
{
    String name;                      //1
    public  String getName()
    {
        return name;
    }

    public abstract int getCost();
}

class HandPancake_Big extends HandPancake
{
    HandPancake_Big()         //2.通过构造器赋值
    {
        name="大份手抓饼";
    }


    @Override
    public int getCost() {
        return 10;
    }
}

class HandPancake_Mid extends HandPancake
{
    HandPancake_Mid()         //2.通过构造器赋值
    {
        name="中份手抓饼";
    }


    @Override
    public int getCost() {
        return 8;
    }
}

abstract class Condiments  extends HandPancake   //3.定义抽象接口
{
    public abstract String getName();
}

class Bacon extends Condiments     //4.继承抽象接口
{
    private HandPancake handPancake;

    Bacon(HandPancake handPancake)
    {
        this.handPancake=handPancake;
    }

    @Override
    public String getName() {
        return handPancake.getName()+"加培根";
    }

    @Override
    public int getCost() {
        return handPancake.getCost()+1;
    }
}
class Cucumber extends Condiments
{
    private HandPancake handPancake;

    Cucumber(HandPancake handPancake)
    {
        this.handPancake=handPancake;
    }

    @Override
    public String getName() {
        return handPancake.getName()+"加黄瓜";
    }

    @Override
    public int getCost() {
        return handPancake.getCost()+2;
    }
}
class Ham extends Condiments
{
    private HandPancake handPancake;

    Ham(HandPancake handPancake)
    {
        this.handPancake=handPancake;
    }

    @Override
    public String getName() {
        return handPancake.getName()+"加火腿";
    }

    @Override
    public int getCost() {
        return handPancake.getCost()+1;
    }
}


public class APPlication
{
    public static void main(String[] args) {
        HandPancake handPancake_big = new HandPancake_Big();

        System.out.println("啥也不加"+handPancake_big.getName()+":"+handPancake_big.getCost());

        handPancake_big = new Ham(handPancake_big);

        System.out.println(handPancake_big.getName()+":"+handPancake_big.getCost());

        handPancake_big = new Cucumber(handPancake_big);

        System.out.println(handPancake_big.getName()+":"+handPancake_big.getCost());

        handPancake_big = new Bacon(handPancake_big);

        System.out.println(handPancake_big.getName()+":"+handPancake_big.getCost());

        System.out.println("==============================");
        HandPancake handPancake_mid = new HandPancake_Mid();
        System.out.println("啥也不加"+handPancake_mid.getName()+":"+handPancake_mid.getCost());

        handPancake_mid = new Ham(handPancake_mid);

        System.out.println(handPancake_mid.getName()+":"+handPancake_mid.getCost());

        handPancake_mid = new Cucumber(handPancake_mid);

        System.out.println(handPancake_mid.getName()+":"+handPancake_mid.getCost());

        handPancake_mid = new Bacon(handPancake_mid);

        System.out.println(handPancake_mid.getName()+":"+handPancake_mid.getCost());


    }
}

手抓饼的扩展性

• 创建手抓饼的种类
• 创建配料种类

官方的扩展：创建一个小份手抓饼继承Hanpancake，然后创建配料继承Condiments。

贴一下直接继承HandPancake的情况：

class HandPancake_Smalll extends HandPancake
class Egg extends HandPancake

abstract class HandPancake
{
    public abstract String getName();

    public abstract int getCost();
}

class HandPancake_Big extends HandPancake
{
    @Override
    public String getName() {
        return "大份手抓饼";
    }

    @Override
    public int getCost() {
        return 10;
    }
}

class HandPancake_Mid extends HandPancake
{
    @Override
    public String getName() {
        return "中份手抓饼";
    }

    @Override
    public int getCost() {
        return 8;
    }
}
class Bacon extends HandPancake
{
    private HandPancake handPancake;

    Bacon(HandPancake handPancake)
    {
        this.handPancake=handPancake;
    }

    @Override
    public String getName() {
        return handPancake.getName()+"加培根";
    }

    @Override
    public int getCost() {
        return handPancake.getCost()+1;
    }
}
class Cucumber extends HandPancake
{
    private HandPancake handPancake;

    Cucumber(HandPancake handPancake)
    {
        this.handPancake=handPancake;
    }

    @Override
    public String getName() {
        return handPancake.getName()+"加黄瓜";
    }

    @Override
    public int getCost() {
        return handPancake.getCost()+2;
    }
}
class Ham extends HandPancake
{
    private HandPancake handPancake;

    Ham(HandPancake handPancake)
    {
        this.handPancake=handPancake;
    }

    @Override
    public String getName() {
        return handPancake.getName()+"加火腿";
    }

    @Override
    public int getCost() {
        return handPancake.getCost()+1;
    }
}
//========================

class HandPancake_Smalll extends HandPancake
{
    @Override
    public String getName() {
        return "小份手抓饼";
    }

    @Override
    public int getCost() {
        return 5;
    }
}


class Egg extends HandPancake
{
    private HandPancake handPancake;

    Egg(HandPancake handPancake)
    {
        this.handPancake=handPancake;
    }

    @Override
    public String getName() {
        return handPancake.getName()+"加鸡蛋";
    }

    @Override
    public int getCost() {
        return handPancake.getCost()+1;
    }
}


public class APPlication
{
    public static void main(String[] args) {
        HandPancake handPancake_big = new HandPancake_Big();

        System.out.println("啥也不加"+handPancake_big.getName()+":"+handPancake_big.getCost());

        handPancake_big = new Ham(handPancake_big);

        System.out.println(handPancake_big.getName()+":"+handPancake_big.getCost());

        handPancake_big = new Cucumber(handPancake_big);

        System.out.println(handPancake_big.getName()+":"+handPancake_big.getCost());

        handPancake_big = new Bacon(handPancake_big);

        System.out.println(handPancake_big.getName()+":"+handPancake_big.getCost());

        System.out.println("==============================");
        HandPancake handPancake_mid = new HandPancake_Mid();
        System.out.println("啥也不加"+handPancake_mid.getName()+":"+handPancake_mid.getCost());

        handPancake_mid = new Ham(handPancake_mid);

        System.out.println(handPancake_mid.getName()+":"+handPancake_mid.getCost());

        handPancake_mid = new Cucumber(handPancake_mid);

        System.out.println(handPancake_mid.getName()+":"+handPancake_mid.getCost());

        handPancake_mid = new Bacon(handPancake_mid);

        System.out.println(handPancake_mid.getName()+":"+handPancake_mid.getCost());


        System.out.println("扩展性测试:");

        HandPancake handPancake_small = new HandPancake_Smalll();
        System.out.println("啥也不加"+handPancake_small.getName()+":"+handPancake_small.getCost());

        handPancake_small = new Egg(handPancake_small);

        System.out.println(handPancake_small.getName()+":"+handPancake_small.getCost());






    }
}

运行结果：