步步为营 .NET 代码重构学习笔记系列

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_BND)   charge=quantity*_winterRate+_winterServiceCharge;else    charge=quantity*_summerRate;
    

改为

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

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;            else                total = price * 0.98;            sendMail();