步步为营 .NET 代码重构学习笔记系列

步步为营 .NET 代码重构学习笔记 一、为何要代码重构

步步为营 .NET 代码重构学习笔记 二、提炼方法(Extract Method)

步步为营 .NET 代码重构学习笔记 三、内联方法(Inline Method)

步步为营 .NET 代码重构学习笔记 四、临时变量(Temporary Variable)

步步为营 .NET 代码重构学习笔记 五、分解函数和替换算法(Replace Method And Substitute Algorithm)

步步为营 .NET 代码重构学习笔记 六、移动函数和移动值域(Move Method And Move Field)

步步为营 .NET 代码重构学习笔记 七

步步为营 .NET 代码重构学习笔记 八

步步为营 .NET 代码重构学习笔记 九

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

    public class Employee{private int _type;public static int ENGINEER = 0;public static int SALEMAN = 1;public static int MANAGER = 2;public Employee(int type){_type = type;}}

改为

    public class Employee{private int _type;public static int ENGINEER = 0;public static int SALEMAN = 1;public static int MANAGER = 2;public Employee(int type){_type = type;}public int Type{get { return _type; }set { _type = value; }}}public class ENGINEER : Employee{public int GetType(){return Employee.ENGINEER;}}public class SALEMAN : Employee{public int GetType(){return Employee.SALEMAN;}}public class MANAGER : Employee{public int GetType(){return Employee.MANAGER;}}public class Factory:Employee{public Employee Create(int type){switch (type){case ENGINEER:return new ENGINEER();case SALEMAN:return new SALEMAN();case MANAGER:return new MANAGER();default:throw new ExecutionEngineException("Incorrect type code value");}}}

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

    public class Employee{private int _type;public static int ENGINEER = 0;public static int SALEMAN = 1;public static int MANAGER = 2;public Employee(int type){_type = type;}public int Type{get { return _type; }set { _type = value; }}public int PayAmount(){switch (_type){case ENGINEER:return 100;case SALEMAN:return 1000;case MANAGER:return 10000;default:throw new ExecutionEngineException("Incorrect type code value");}}}

改为

    public class Employee{private int _type;public static int ENGINEER = 0;public static int SALEMAN = 1;public static int MANAGER = 2;public Employee(int type){_type = type;}public int Type{get { return _type; }set { _type = value; }}public int PayAmount(){EmployeeType employeeType;switch (_type){case ENGINEER:employeeType= new ENGINEER();break;case SALEMAN:employeeType=new SALEMAN();break;case MANAGER:employeeType = new MANAGER();break;default:throw new ExecutionEngineException("Incorrect type code value");}return employeeType.GetType();}}public class ENGINEER : EmployeeType{public override  int GetType(){return 100;}}public class SALEMAN : EmployeeType{public override int GetType(){return 1000;}}public class MANAGER : EmployeeType{public override int GetType(){return 10000;}}public abstract class EmployeeType{public abstract int GetType();}

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

    public abstract class Person{public  abstract bool IsMale();public  abstract string GetCode();public Person CreateMale(){return new  Male();}public Person CreateFemale(){return new Female();}}public class Male : Person{public override bool IsMale(){return true;}public override string GetCode(){return "M";}}public class Female : Person{public override bool IsMale(){return false;}public override string GetCode(){return "F";}}

改为

    public class Person{private bool _IsMale;private string _Code;public bool IsMale{get { return _IsMale; }set { _IsMale = value; }}public string Code{get { return _Code; }set { _Code = value; }}public Person(bool isMale, string code){this._IsMale = isMale;this._Code = code;}}public class Male : Person{public Male(): base(true, "M"){ }}public class Female : Person{public Female(): base(false, "F"){ }}

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

if(date<SUMMER_START||date>SUMMER_BND)charge=quantity*_winterRate+_winterServiceCharge;
elsecharge=quantity*_summerRate;

改为

if(notSummer(date))charge=winterCharge(quantity);
elsecharge=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

        public double DisabilityAmount(){if (_seniority < 2) return 0;if (_monthsDisabled > 12) return 0;if (_isPartTime) return 0;return 1;}

改为

        public double DisabilityAmount(){if (IsNotBligableForDisability()) return 0;return 1;}

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

            if (isSpecialDeal()){total = price * 0.95;sendMail();}else{total = price * 0.98;sendMail();}

改为

            if (isSpecialDeal())total = price * 0.95;elsetotal = price * 0.98;sendMail();