[Reprinted] Reading Notes on restructuring-improving the design of existing code

Reposted from: http://www.cnblogs.com/karoc/archive/2011/09/16/2179125.html#2497969. Thanks to the original author.

 

Bad taste	Features	Situation and Handling Method		Target
Duplicate code	1. repeated expressions 2. Different algorithms do the same thing 3. Similar code	Two Functions of the same class have the same expression.	Repeated code extraction as a method	The same expression only appears in one method of a class for other methods to call.
		Sibling class contains the same expression	Repeated code extraction as a method Upgrade Method to parent class
		Irrelevant classes contain the same code	Extracted as an independent class for calling
Too long Function	1. There are comments before the code 2. conditional expressions 3. Loop		Extraction Method	Each method only does one thing. The method must be well defined and named.
Too large class	1. There are too many instance variables in a class 2. There is too much code in a class	High correlation between some fields	Related Fields and methods are extracted as classes.	Each class is responsible for a group of internally associated tasks.
		Some fields and methods are only used by some instances.	These fields and methods are moved to the subclass.
Too long parameter Column	1. The parameter column is too long. 2. Frequent parameter column changes	You can use other methods to obtain this parameter.	Allow the parameter recipient to obtain the parameter.	You just need to pass the function enough to get what you need from it.
		Several attributes of the same object as parameters	Use the entire object as a parameter without deteriorating Dependencies
		The called function uses many attributes of another object.	Move the method to this object
		Some data lacks owner objects	First create an object
Divergent changes	A class is affected by various changes.	Classes often change in different directions for different reasons.	Extract all changes caused by specific reasons into a new class	All modifications to an external change should only occur in a single class, And all content in this class should reflect this change.
Flexible Modification	One change causes the modification of multiple classes.	Some changes require small modifications in many different classes.	Put all the code to be modified into the same class	All modifications to an external change should only occur in a single class, And all content in this class should reflect this change.
Attachment Complex	A function uses more class attributes than its own class attributes.	A function calls almost half-dozen value functions from another object.	Extract the attachment code as a separate method and move it to another object.	Package data and data operations
Data dashboard	The data used at the same time is not organized as a class. 1. The same fields in the two classes 2. Same parameters in many functions		Extract fields as classes, and then reduce the parameters in the function signature.	Data that is always tied together should have their own objects
Basic Type paranoia	Excessive use of Basic Types	Basic type fields that are always put together	Extraction class	Convert an existing data value to an object
		The parameter columns have basic types.	Extract parameter objects
		The array contains different objects and data needs to be selected from the array.	Replace arrays with objects
		The basic data is the type code.	Use class replacement type code
		Type Code with conditional expression	Replace type codes with inheritance classes
Switch statement	The same switch and case statements are distributed in different places.	Switch selected based on the Type Code	Replace switch with Polymorphism	Avoid making the same changes everywhere
		Switch exists in a single function	Replace parameters with explicit methods
Parallel Inheritance System	1. When adding a subclass to a class, you must add a subclass to another class. 2. the prefix of an inherited system class name is the same as that of another inherited system class name.		Instances in one inheritance system reference instances in another inheritance system, and then migrate members	Avoid making the same changes everywhere
Redundancy	Class idle	There is no big difference between the parent class and the subclass.	Integrate them into one
		A class does not do much.	Move all the members of this class to another class and delete it.
Talking about the future		An abstract class does not have much effect.	Merge Parent and Child classes
		Unnecessary Delegation	Move all the members of this class to another class and delete it.
		Some parameters of the function are not used.	Remove Parameters
		Function names have redundant abstraction meanings	Rename function name
		The function is called only by the test method.	Delete together with test code
Confusing temporary Fields	1. An Instance field is set only in some situations 2. Some instance fields are set only for complex algorithms that do not pass parameters to a function.		Extract separate classes and encapsulate related Code
Over-coupling message chain	A long string of getthis or temporary variables	The customer class acquires another object through one delegate class.	Hide Delegation	Eliminate coupling
Intermediary	A class interface has a large number of functions that are delegated to other classes.	Half of the Functions	Remove man-in-the-middle
		A few functions	Direct call
		Man-in-the-middle has other behaviors	Let the delegate class inherit the delegate class
Relationship	A class needs to know the private members of another class.	Sub-classes over-understand superclasses	Change inheritance to delegate and remove sub-classes from the inheritance system	Encapsulation
		Bidirectional association between classes	Remove unnecessary associations
		Classes have something in common	Extract new classes
Similar class	The two functions do the same thing, but the signatures are different.		Merge
Imperfect Class Libraries	Class Library functions are not well constructed and cannot be modified.	Want to modify one or two functions	Add a function in the call class
		Want to add a bunch of additional Behaviors	Use subclass or package class
Naive data	In addition to fields, a class is a field accessor or configurator.		1. Replace the public field with an accessors 2. encapsulate the set properly 3. Remove unnecessary seters 4. Move the method called by the accessor and setter to this class. 5. Hide accessors and seters	Encapsulation
Rejected gifts	The derived class only uses a few member functions of the base class.	The subclass rejects the inheritance of the superclass interface.	Use delegation to replace inheritance
Too many comments	A piece of code has long comments		Eliminate various bad tastes