步步为营 .NET 代码重构学习笔记 十

一、Replace Type Code with Subclasses （以子类取代型别码）

动机（Motivation）

以 一个subclass取代这个type code，如果面对的type code不会影响宿主类的行为，可以使用Replace Type Code with Class 来处理它们。但如果type code 会影响宿主类的行为，那么最好的办法就是借助多态（polymorphism）业处理 变化行为。

示例

01 public class Employee
02 {
03     private int _type;
04     public static int ENGINEER = 0;
05     public static int SALEMAN = 1;
06     public static int MANAGER = 2;
07
08     public Employee(int type)
09     {
10         _type = type;
11     }
12 }

改为

01 public class Employee
02 {
03     private int _type;
04     public static int ENGINEER = 0;
05     public static int SALEMAN = 1;
06     public static int MANAGER = 2;
07
08     public Employee(int type)
09     {
10         _type = type;
11     }
12
13     public int Type
14     {
15         get { return _type; }
16         set { _type = value; }
17     }
18
19
20 }
21
22 public class ENGINEER : Employee
23 {
24     public int GetType()
25     {
26         return Employee.ENGINEER;
27     }
28 }
29
30 public class SALEMAN : Employee
31 {
32     public int GetType()
33     {
34         return Employee.SALEMAN;
35     }
36 }
37
38 public class MANAGER : Employee
39 {
40     public int GetType()
41     {
42         return Employee.MANAGER;
43     }
44 }
45
46 public class Factory:Employee
47 {
48     public Employee Create(int type)
49     {
50         switch (type)
51         {
52             case ENGINEER:
53                 return new ENGINEER();
54             case SALEMAN:
55                 return new SALEMAN();
56             case MANAGER:
57                 return new MANAGER();
58             default:
59                 throw new ExecutionEngineException("Incorrect type code value");
60         }
61     }
62 }

二、Replace Type Code with State/Strategy（以State/Strategy取代型别码）

动机（Motivation）

以State object（专门用来描述状态的对象）取代type code。

示例

01 public class Employee
02 {
03     private int _type;
04     public static int ENGINEER = 0;
05     public static int SALEMAN = 1;
06     public static int MANAGER = 2;
07
08     public Employee(int type)
09     {
10         _type = type;
11     }
12
13     public int Type
14     {
15         get { return _type; }
16         set { _type = value; }
17     }
18
19     public int PayAmount()
20     {
21         switch (_type)
22         {
23             case ENGINEER:
24                 return 100;
25             case SALEMAN:
26                 return 1000;
27             case MANAGER:
28                 return 10000;
29             default:
30                 throw new ExecutionEngineException("Incorrect type code value");
31         }
32     }
33
34 }

改为

01 public class Employee
02 {
03     private int _type;
04     public static int ENGINEER = 0;
05     public static int SALEMAN = 1;
06     public static int MANAGER = 2;
07
08     public Employee(int type)
09     {
10         _type = type;
11     }
12
13     public int Type
14     {
15         get { return _type; }
16         set { _type = value; }
17     }
18
19     public int PayAmount()
20     {
21         EmployeeType employeeType;
22         switch (_type)
23         {
24             case ENGINEER:
25                 employeeType= new ENGINEER();
26                 break;
27             case SALEMAN:
28                 employeeType=new SALEMAN();
29                 break;
30             case MANAGER:
31                 employeeType = new MANAGER();
32                 break;
33             default:
34                 throw new ExecutionEngineException("Incorrect type code value");
35         }
36         return employeeType.GetType();
37     }
38
39 }
40
41 public class ENGINEER : EmployeeType
42 {
43     public override  int GetType()
44     {
45         return 100;
46     }
47 }
48
49 public class SALEMAN : EmployeeType
50 {
51     public override int GetType()
52     {
53         return 1000;
54     }
55 }
56
57 public class MANAGER : EmployeeType
58 {
59     public override int GetType()
60     {
61         return 10000;
62     }
63 }
64
65 public abstract class EmployeeType
66 {
67     public abstract int GetType();
68
69 }

三、Replace Subclass with Fields（以值域取代子类）

动机（Motivation）

修改这些函数，使它们返回superclass中的某个（新增值域，然后销毁subclasses）

示例

01 public abstract class Person
02 {
03    public  abstract bool IsMale();
04    public  abstract string GetCode();
05
06    public Person CreateMale()
07    {
08        return new  Male();
09    }
10
11    public Person CreateFemale()
12    {
13        return new Female();
14    }
15 }
16
17 public class Male : Person
18 {
19
20     public override bool IsMale()
21     {
22         return true;
23     }
24
25     public override string GetCode()
26     {
27         return "M";
28     }
29 }
30
31 public class Female : Person
32 {
33
34     public override bool IsMale()
35     {
36         return false;
37     }
38
39     public override string GetCode()
40     {
41         return "F";
42     }
43 }

改为

01 public class Person
02 {
03     private bool _IsMale;
04     private string _Code;
05
06     public bool IsMale
07     {
08         get { return _IsMale; }
09         set { _IsMale = value; }
10     }
11
12     public string Code
13     {
14         get { return _Code; }
15         set { _Code = value; }
16     }
17     public Person(bool isMale, string code)
18     {
19         this._IsMale = isMale;
20         this._Code = code;
21     }
22 }
23
24 public class Male : Person
25 {
26
27     public Male()
28         : base(true, "M")
29     { }
30 }
31
32 public class Female : Person
33 {
34     public Female()
35         : base(false, "F")
36     { }
37 }

四、Decompose Conditional（分解条件式）

动机（Motivation）

从if、then、else三个段落中分别提炼出独立函数。

示例

1 if(date<SUMMER_START||date>SUMMER_BND)
2    charge=quantity*_winterRate+_winterServiceCharge;
3 else
4     charge=quantity*_summerRate;

改为

1 if(notSummer(date))
2    charge=winterCharge(quantity);
3 else
4     charge=summerCharge(quantity);

五、Consolidate Conditional Expression（合并条件式）

动机（Motivation）

将很多条件合并成一个条件式，并将这个条件式提炼成为一个独立函数。

示例

1 public double DisabilityAmount()
2 {
3     if (_seniority < 2) return 0;
4     if (_monthsDisabled > 12) return 0;
5     if (_isPartTime) return 0;
6     return 1;
7 }

改为

1 public double DisabilityAmount()
2 {
3     if (IsNotBligableForDisability()) return 0;
4     return 1;
5 }

六、Consolidate Duplicate Conditional Fragments（合并重复的条件片段）

动机（Motivation）

将重复代码搬移到条件式之外。

示例

01 if (isSpecialDeal())
02 {
03     total = price * 0.95;
04     sendMail();
05 }
06 else
07 {
08     total = price * 0.98;
09     sendMail();
10 }

改为

view source print ?

1	if (isSpecialDeal())

2	total = price * 0.95;

3

else

4	total = price * 0.98;

5

6	sendMail();