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*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：