第一章.良好应用程序基石

Posted 2020-09-28 lanshanxiao

伟大软件的简易三步骤：

1.确认你的软件客户要它做的事。

2.运用基本的OO原则来增加软件的灵活性。

3.努力实现可维护、可重用的设计。

项目架构：

Guitar类：

 1 package com.headfirst.guitar;
 2 
 3 public class Guitar {
 4     private String serialNumber, builder, model, type, backWood, topWood;
 5     private double price;
 6     
 7     public Guitar(String serialNumber, double price, String builder, 
 8             String model, String type, String backWood, String topWood){
 9         this.serialNumber = serialNumber;
10         this.price = price;
11         this.builder = builder;
12         this.model = model;
13         this.type = type;
14         this.backWood = backWood;
15         this.topWood = topWood;
16     }
17     
18     public String getSerialNumber(){
19         return serialNumber;
20     }
21     public double getPrice(){
22         return price;
23     }
24     public void setPrice(float newPrice){
25         this.price = newPrice;
26     }
27     public String getBuilder(){
28         return builder;
29     }
30     public String getModel(){
31         return model;
32     }
33     public String getType(){
34         return type;
35     }
36     public String getBackWood(){
37         return backWood;
38     }
39     public String getTopWood(){
40         return topWood;
41     }
42 }

Inventory类：

 1 package com.headfirst.guitar;
 2 
 3 import java.util.Iterator;
 4 import java.util.LinkedList;
 5 import java.util.List;
 6 
 7 public class Inventory {
 8     
 9     private List guitars;
10     
11     public Inventory(){
12         guitars = new LinkedList();
13     }
14     
15     public void addGuitar(String serialNumber, double price, String builder, String model, String type,
16             String backWood, String topWood){
17         Guitar guitar = new Guitar(serialNumber, price, builder, 
18                 model, type, backWood, topWood);
19         guitars.add(guitar);
20     }
21     
22     public Guitar getGuitar(String serialNumber){
23         for(Iterator i = guitars.iterator(); i.hasNext();){
24             Guitar guitar = (Guitar) i.next();
25             if(guitar.getSerialNumber().equals(serialNumber)){
26                 return guitar;
27             }
28         }
29         
30         return null;
31     }
32     
33     public Guitar search(Guitar searchGuitar){
34         for(Iterator i = guitars.iterator(); i.hasNext();){
35             Guitar guitar = (Guitar) i.next();
36             String builder = searchGuitar.getBuilder();
37             if((builder != null) && (!builder.equals("")) && 
38                     (!builder.equals(guitar.getBuilder())))
39                     continue;
40             
41             String model = searchGuitar.getModel();
42             if((model != null) && (!model.equals("")) && 
43                     (!model.equals(guitar.getModel())))
44                     continue;
45             
46             String type = searchGuitar.getType();
47             if((type != null) && (!type.equals("")) && 
48                     (!type.equals(guitar.getType())))
49                     continue;
50             
51             String backWood = searchGuitar.getBackWood();
52             if((backWood != null) && (!backWood.equals("")) && 
53                     (!backWood.equals(guitar.getBackWood())))
54                     continue;
55             
56             String topWood = searchGuitar.getTopWood();
57             if((topWood != null) && (!topWood.equals("")) && 
58                     (!topWood.equals(guitar.getTopWood())))
59                     continue;
60             return guitar;
61         }
62         
63         return null;
64     }
65 }

搜寻测试代码：

 1 package com.headfirst.guitar;
 2 
 3 public class FindGuitarTester {
 4     public static void main(String[] args){
 5         Inventory inventory = new Inventory();
 6         initializeInventory(inventory);
 7         
 8         Guitar whatErinLikes = new Guitar("", 0, "fender", "Stratocastor", "electric", "Alder", "Alder");
 9         
10         Guitar guitar = inventory.search(whatErinLikes);
11         if(guitar != null){
12             System.out.println("Erin, you might like this " + 
13             guitar.getBuilder() + " " + guitar.getModel() + 
14             " " + guitar.getType() + " guitar:\\n " + 
15             guitar.getBackWood() + " back and sides,\\n " +
16             guitar.getTopWood() + " top.\\nYou can have it for only $" + 
17             guitar.getPrice() + "!");
18         }else{
19             System.out.println("Sorry, Erin, we have nothing for you.");
20         }
21     }
22     
23     private static void initializeInventory(Inventory inventory){
24         inventory.addGuitar("V95693", 1499.95, "Fender", "Stratocastor", "electric", "Alder", "Alder");
25     }
26 }

运行结果：

为什么，明明有，为什么说没有?

检查了代码，可能搜寻中“fender”的f是小写，而我们有的“Fender”是大写。

好，我们对吉他搜索工具进行第一个改善，去除掉所有String比较：

项目修改架构：

Builder.java：

 1 package com.headfirst.guitar;
 2 
 3 public enum Builder {
 4     
 5     FENDER, MARTIN, GIBSON, COLLINGS, OLSON, RYAN, PRS, ANY;
 6     
 7     public String toString(){
 8         switch(this){
 9         case FENDER:
10             return "Fender";
11         case MARTIN:
12             return "Martin";
13         case GIBSON:
14             return "Gibson";
15         case COLLINGS:
16             return "Collings";
17         case OLSON:
18             return "Olson";
19         case RYAN:
20             return "Ryan";
21         case PRS:
22             return "Prs";
23         case ANY:
24             return "Any";
25         default: 
26             return "";
27         }
28     }
29 }

Type.java：

 1 package com.headfirst.guitar;
 2 
 3 public enum Type {
 4     ACOUSTIC, ELECTRIC;
 5     
 6     public String toString(){
 7         switch(this){
 8         case ACOUSTIC: 
 9             return "acoustic";
10         case ELECTRIC: 
11             return "electric";
12         default:
13             return "";
14         }
15     }
16 }

Wood.java：

 1 package com.headfirst.guitar;
 2 
 3 public enum Wood {
 4     INDIAN_ROSEWOOD, BRAZILIAN_ROSEWOOD, ALDER;
 5     
 6     public String toString(){
 7         switch(this){
 8         case INDIAN_ROSEWOOD:
 9             return "Indian Rosewood";
10         case BRAZILIAN_ROSEWOOD:
11             return "Brazilian Rosewood";
12         case ALDER:
13             return "Alder";
14         default:
15             return "";
16         }
17     }
18 }

修改FindGuitarTester.java第8行代码：

 1 Guitar whatErinLikes = new Guitar("", 0, "Builder.FENDER", "Stratocastor", "Type.ELECTRIC", "Wood.ALDER", "Wood.ALDER"); 

修改Inventory.java中search()方法：

 1 public Guitar search(Guitar searchGuitar){
 2         for(Iterator i = guitars.iterator(); i.hasNext();){
 3             Guitar guitar = (Guitar) i.next();
 4             
 5             if(searchGuitar.getBuilder() != guitar.getBuilder())
 6                     continue;
 7             
 8             String model = searchGuitar.getModel().toLowerCase();
 9             if((model != null) && (!model.equals("")) && 
10                     (!model.equals(guitar.getModel().toLowerCase())))
11                     continue;
12             
13             if(searchGuitar.getType() != guitar.getType())
14                     continue;
15             
16             if(searchGuitar.getBackWood() != guitar.getBackWood())
17                     continue;
18             
19             if(searchGuitar.getTopWood() != guitar.getTopWood())
20                     continue;
21             
22             return guitar;
23         }
24         
25         return null;
26     }

现在我们担心的是Model属性，我们没有把它做成enum，并且Model没有办法限制，所以做不出enum。

除此之外：我们修改的地方还有：

各种变量的类型，用enum的全部替换掉。