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结构型模式————装饰器模式（3.1）
来源：cnblogs　　作者：noneplus　　时间：2019/8/15 12:15:02　　对本文有异议

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：

  1. abstract class HandPancake
  2. {
  3.     public abstract String getName();
  5.     public abstract int getCost();
  6. }
  8. class HandPancake_Big extends HandPancake
  9. {
  10.     @Override
  11.     public String getName() {
  12.         return "大份手抓饼";
  13.     }
  15.     @Override
  16.     public int getCost() {
  17.         return 10;
  18.     }
  19. }
  21. class HandPancake_Mid extends HandPancake
  22. {
  23.     @Override
  24.     public String getName() {
  25.         return "中份手抓饼";
  26.     }
  28.     @Override
  29.     public int getCost() {
  30.         return 8;
  31.     }
  32. }
  33. class Bacon extends HandPancake
  34. {
  35.     private HandPancake handPancake;
  37.     Bacon(HandPancake handPancake)
  38.     {
  39.         this.handPancake=handPancake;
  40.     }
  42.     @Override
  43.     public String getName() {
  44.         return handPancake.getName()+"加培根";
  45.     }
  47.     @Override
  48.     public int getCost() {
  49.         return handPancake.getCost()+1;
  50.     }
  51. }
  52. class Cucumber extends HandPancake
  53. {
  54.     private HandPancake handPancake;
  56.     Cucumber(HandPancake handPancake)
  57.     {
  58.         this.handPancake=handPancake;
  59.     }
  61.     @Override
  62.     public String getName() {
  63.         return handPancake.getName()+"加黄瓜";
  64.     }
  66.     @Override
  67.     public int getCost() {
  68.         return handPancake.getCost()+2;
  69.     }
  70. }
  71. class Ham extends HandPancake
  72. {
  73.     private HandPancake handPancake;
  75.     Ham(HandPancake handPancake)
  76.     {
  77.         this.handPancake=handPancake;
  78.     }
  80.     @Override
  81.     public String getName() {
  82.         return handPancake.getName()+"加火腿";
  83.     }
  85.     @Override
  86.     public int getCost() {
  87.         return handPancake.getCost()+1;
  88.     }
  89. }
  92. public class APPlication
  93. {
  94.     public static void main(String[] args) {
  95.         HandPancake handPancake_big = new HandPancake_Big();
  97.         System.out.println("啥也不加"+handPancake_big.getName()+":"+handPancake_big.getCost());
  99.         handPancake_big = new Ham(handPancake_big);
  101.         System.out.println(handPancake_big.getName()+":"+handPancake_big.getCost());
  103.         handPancake_big = new Cucumber(handPancake_big);
  105.         System.out.println(handPancake_big.getName()+":"+handPancake_big.getCost());
  107.         handPancake_big = new Bacon(handPancake_big);
  109.         System.out.println(handPancake_big.getName()+":"+handPancake_big.getCost());
  111.         System.out.println("==============================");
  112.         HandPancake handPancake_mid = new HandPancake_Mid();
  113.         System.out.println("啥也不加"+handPancake_mid.getName()+":"+handPancake_mid.getCost());
  115.         handPancake_mid = new Ham(handPancake_mid);
  117.         System.out.println(handPancake_mid.getName()+":"+handPancake_mid.getCost());
  119.         handPancake_mid = new Cucumber(handPancake_mid);
  121.         System.out.println(handPancake_mid.getName()+":"+handPancake_mid.getCost());
  123.         handPancake_mid = new Bacon(handPancake_mid);
  125.         System.out.println(handPancake_mid.getName()+":"+handPancake_mid.getCost());
  128.     }
  129. }

1565696683438

官方做法：

  1. abstract class HandPancake
  2. {
  3.     String name;                      //1
  4.     public  String getName()
  5.     {
  6.         return name;
  7.     }
  9.     public abstract int getCost();
  10. }
  12. class HandPancake_Big extends HandPancake
  13. {
  14.     HandPancake_Big()         //2.通过构造器赋值
  15.     {
  16.         name="大份手抓饼";
  17.     }
  20.     @Override
  21.     public int getCost() {
  22.         return 10;
  23.     }
  24. }
  26. class HandPancake_Mid extends HandPancake
  27. {
  28.     HandPancake_Mid()         //2.通过构造器赋值
  29.     {
  30.         name="中份手抓饼";
  31.     }
  34.     @Override
  35.     public int getCost() {
  36.         return 8;
  37.     }
  38. }
  40. abstract class Condiments  extends HandPancake   //3.定义抽象接口
  41. {
  42.     public abstract String getName();
  43. }
  45. class Bacon extends Condiments     //4.继承抽象接口
  46. {
  47.     private HandPancake handPancake;
  49.     Bacon(HandPancake handPancake)
  50.     {
  51.         this.handPancake=handPancake;
  52.     }
  54.     @Override
  55.     public String getName() {
  56.         return handPancake.getName()+"加培根";
  57.     }
  59.     @Override
  60.     public int getCost() {
  61.         return handPancake.getCost()+1;
  62.     }
  63. }
  64. class Cucumber extends Condiments
  65. {
  66.     private HandPancake handPancake;
  68.     Cucumber(HandPancake handPancake)
  69.     {
  70.         this.handPancake=handPancake;
  71.     }
  73.     @Override
  74.     public String getName() {
  75.         return handPancake.getName()+"加黄瓜";
  76.     }
  78.     @Override
  79.     public int getCost() {
  80.         return handPancake.getCost()+2;
  81.     }
  82. }
  83. class Ham extends Condiments
  84. {
  85.     private HandPancake handPancake;
  87.     Ham(HandPancake handPancake)
  88.     {
  89.         this.handPancake=handPancake;
  90.     }
  92.     @Override
  93.     public String getName() {
  94.         return handPancake.getName()+"加火腿";
  95.     }
  97.     @Override
  98.     public int getCost() {
  99.         return handPancake.getCost()+1;
  100.     }
  101. }
  104. public class APPlication
  105. {
  106.     public static void main(String[] args) {
  107.         HandPancake handPancake_big = new HandPancake_Big();
  109.         System.out.println("啥也不加"+handPancake_big.getName()+":"+handPancake_big.getCost());
  111.         handPancake_big = new Ham(handPancake_big);
  113.         System.out.println(handPancake_big.getName()+":"+handPancake_big.getCost());
  115.         handPancake_big = new Cucumber(handPancake_big);
  117.         System.out.println(handPancake_big.getName()+":"+handPancake_big.getCost());
  119.         handPancake_big = new Bacon(handPancake_big);
  121.         System.out.println(handPancake_big.getName()+":"+handPancake_big.getCost());
  123.         System.out.println("==============================");
  124.         HandPancake handPancake_mid = new HandPancake_Mid();
  125.         System.out.println("啥也不加"+handPancake_mid.getName()+":"+handPancake_mid.getCost());
  127.         handPancake_mid = new Ham(handPancake_mid);
  129.         System.out.println(handPancake_mid.getName()+":"+handPancake_mid.getCost());
  131.         handPancake_mid = new Cucumber(handPancake_mid);
  133.         System.out.println(handPancake_mid.getName()+":"+handPancake_mid.getCost());
  135.         handPancake_mid = new Bacon(handPancake_mid);
  137.         System.out.println(handPancake_mid.getName()+":"+handPancake_mid.getCost());
  140.     }
  141. }

1565696715504

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

  1. abstract class HandPancake
  2. {
  3.     public abstract String getName();
  5.     public abstract int getCost();
  6. }
  8. class HandPancake_Big extends HandPancake
  9. {
  10.     @Override
  11.     public String getName() {
  12.         return "大份手抓饼";
  13.     }
  15.     @Override
  16.     public int getCost() {
  17.         return 10;
  18.     }
  19. }
  21. class HandPancake_Mid extends HandPancake
  22. {
  23.     @Override
  24.     public String getName() {
  25.         return "中份手抓饼";
  26.     }
  28.     @Override
  29.     public int getCost() {
  30.         return 8;
  31.     }
  32. }
  33. class Bacon extends HandPancake
  34. {
  35.     private HandPancake handPancake;
  37.     Bacon(HandPancake handPancake)
  38.     {
  39.         this.handPancake=handPancake;
  40.     }
  42.     @Override
  43.     public String getName() {
  44.         return handPancake.getName()+"加培根";
  45.     }
  47.     @Override
  48.     public int getCost() {
  49.         return handPancake.getCost()+1;
  50.     }
  51. }
  52. class Cucumber extends HandPancake
  53. {
  54.     private HandPancake handPancake;
  56.     Cucumber(HandPancake handPancake)
  57.     {
  58.         this.handPancake=handPancake;
  59.     }
  61.     @Override
  62.     public String getName() {
  63.         return handPancake.getName()+"加黄瓜";
  64.     }
  66.     @Override
  67.     public int getCost() {
  68.         return handPancake.getCost()+2;
  69.     }
  70. }
  71. class Ham extends HandPancake
  72. {
  73.     private HandPancake handPancake;
  75.     Ham(HandPancake handPancake)
  76.     {
  77.         this.handPancake=handPancake;
  78.     }
  80.     @Override
  81.     public String getName() {
  82.         return handPancake.getName()+"加火腿";
  83.     }
  85.     @Override
  86.     public int getCost() {
  87.         return handPancake.getCost()+1;
  88.     }
  89. }
  90. //========================
  92. class HandPancake_Smalll extends HandPancake
  93. {
  94.     @Override
  95.     public String getName() {
  96.         return "小份手抓饼";
  97.     }
  99.     @Override
  100.     public int getCost() {
  101.         return 5;
  102.     }
  103. }
  106. class Egg extends HandPancake
  107. {
  108.     private HandPancake handPancake;
  110.     Egg(HandPancake handPancake)
  111.     {
  112.         this.handPancake=handPancake;
  113.     }
  115.     @Override
  116.     public String getName() {
  117.         return handPancake.getName()+"加鸡蛋";
  118.     }
  120.     @Override
  121.     public int getCost() {
  122.         return handPancake.getCost()+1;
  123.     }
  124. }
  127. public class APPlication
  128. {
  129.     public static void main(String[] args) {
  130.         HandPancake handPancake_big = new HandPancake_Big();
  132.         System.out.println("啥也不加"+handPancake_big.getName()+":"+handPancake_big.getCost());
  134.         handPancake_big = new Ham(handPancake_big);
  136.         System.out.println(handPancake_big.getName()+":"+handPancake_big.getCost());
  138.         handPancake_big = new Cucumber(handPancake_big);
  140.         System.out.println(handPancake_big.getName()+":"+handPancake_big.getCost());
  142.         handPancake_big = new Bacon(handPancake_big);
  144.         System.out.println(handPancake_big.getName()+":"+handPancake_big.getCost());
  146.         System.out.println("==============================");
  147.         HandPancake handPancake_mid = new HandPancake_Mid();
  148.         System.out.println("啥也不加"+handPancake_mid.getName()+":"+handPancake_mid.getCost());
  150.         handPancake_mid = new Ham(handPancake_mid);
  152.         System.out.println(handPancake_mid.getName()+":"+handPancake_mid.getCost());
  154.         handPancake_mid = new Cucumber(handPancake_mid);
  156.         System.out.println(handPancake_mid.getName()+":"+handPancake_mid.getCost());
  158.         handPancake_mid = new Bacon(handPancake_mid);
  160.         System.out.println(handPancake_mid.getName()+":"+handPancake_mid.getCost());
  163.         System.out.println("扩展性测试:");
  165.         HandPancake handPancake_small = new HandPancake_Smalll();
  166.         System.out.println("啥也不加"+handPancake_small.getName()+":"+handPancake_small.getCost());
  168.         handPancake_small = new Egg(handPancake_small);
  170.         System.out.println(handPancake_small.getName()+":"+handPancake_small.getCost());
  177.     }
  178. }

运行结果：

1565696654138

原文链接：http://www.cnblogs.com/noneplus/p/11348102.html

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