Refactoring Patterns in Software Engineering: Lecture 10 by Raman Ramsin, Slides of Software Engineering

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Patterns in Software Engineering Lecturer: Raman Ramsin^ Lecture 10^ Refactoring Patterns

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Part^

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Patterns in Software Engineering – Lecture 10 Refactoring: DefinitionRefactoring:

Definition

„^ Refactoring:^

A change made to the internal structure of software tomake it^ „^ easier to understand, and^ „^ cheaper to modify.

^ The observable behavior of the software should not bechanged.

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Patterns in Software Engineering – Lecture 10 Refactoring: Why?Refactoring:

Why?

„^ Why Should You Refactor?^

Refactoring Improves the Design of Software

Refactoring Makes Software Easier to Understand Refactoring Helps You Find Bugs Refactoring Helps You Program Faster

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Patterns in Software Engineering – Lecture 10 Refactoring: When?Refactoring:

When?

„^ When Should You Refactor? „^ When

Should You Refactor?

^ Refactor the third time you do something similar (The Rule ^ Refactor

the third time you do something similar (The Rule

of Three)

Refactor When You Add Function Refactor When You Need to Fix a Bug Refactor As You Do a Code Review

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Patterns in Software Engineering – Lecture 10 Symptoms of Bad Code (1)Symptoms

of Bad Code (1)

1.^ Duplicated Code2.^ Long Method3.^ Large Class

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4.^ Long Parameter ListDi

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5.^ Divergent Change:

When one class is commonly changed in different

ways for different reasons. 6 Shotgun Surgery:

When every time you make a kind of change

you

6.^ Shotgun Surgery:

When

every time you make a kind of change, you

have to make a lot of little changes to a lot of different classes. 7 Feature Envy:

A method that seems more interested in a class other than

7.^ Feature Envy:

A^ method that seems more interested in a class other than the one it actually is in. 8 Data Clumps:

Bunches of data that regularly appear together

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8.^ Data Clumps:

Bunches

of data that regularly appear together.

Patterns in Software Engineering – Lecture 10 Symptoms of Bad Code (2)Symptoms

of Bad Code (2)

9.^ Primitive Obsession:

Excessive use of primitives, due to reluctance to

p^

,

use small objects for small tasks. 10. Switch Statements11. Parallel Inheritance Hierarchies:

Where every time you make a

subclass of one class, you also have to make a subclass of another. 12. Lazy Class:

A class that isn't doing enough to justify its maintenance. 13 Speculative Generality:

Classes and features have been added just

13.^ Speculative Generality:

Classes

and features have been added just

because a need for them may arise someday. 14 Temporary Field:

An instance variable that is set only in certain

14.^ Temporary Field:

An^ instance variable that is set only in certain

circumstances. 15. Message Chains:

Transitive visibility chains.

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15.^ Message

Chains:

Transitive

visibility chains.

Patterns in Software Engineering – Lecture 10 Symptoms of Bad Code (3)Symptoms

of Bad Code (3)

16 Middle Man:

Excessive delegation

16.^ Middle Man:

Excessive

delegation.

17.^ Inappropriate Intimacy:

Excessive interaction and coupling.

18.^ Alternative Classes with Different Interfaces:

Classes that do the

same thing but have different interfaces for what they do. 19. Incomplete Library Class20. Data Class:

Classes that have fields, getting and setting methods for the fields, and nothing else. 21. Refused Bequest:

When subclasses do not fulfill the commitments of

h^

l their superclasses. 22. Comments:

When comments are used to compensate for bad code.

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Patterns in Software Engineering – Lecture 10 Refactoring Patterns: CategoriesRefactoring

Patterns: Categories

„^ Composing Methods:

Packaging code properly

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„^ Moving Features Between Objects:

Reassigning responsibilities

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k^ ith

„^ Organizing Data:

Making data easier to work with

„^ Simplifying Conditional Expressions:

Making conditional logic

less e

o^ p one

less error-prone „ Making Method Calls Simpler:

Making interfaces easy to

understand and useunderstand and use „ Dealing with Generalization:

Moving features around a hierarchy

of inheritanceof inheritance „ Big Refactorings:

Large-scale changes to code

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Patterns in Software Engineering – Lecture 10 Composing Methods:

Extract Method

Composing

Methods:

Extract

Method

„^ Extract Method^ ^

You have a code fragment that can be grouped together You^ have a code fragment that can be grouped together. Turn the fragment into a method whose name explains the purpose of themethod.

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Patterns in Software Engineering – Lecture 10 Composing Methods:

Inline Method

Composing

Methods:

Inline

Method

„^ Inline Method^ ^

A method

's body is just as clear as its name

^ A method s body is just as clear as its name. ^ Put the method's body into the body of its callers and remove the method. Department of Computer Engineering

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Patterns in Software Engineering – Lecture 10 Composing Methods:

Replace Method with Method Object

Composing

Methods:

Replace

Method with Method Object

„^ Replace Method with Method Object^ ^

You have a long method that uses local variables in such a way that you cannot You^ have a long method that uses local variables in such a way that you cannotapplyExtract Method. Turn the method into an object so that all the local variables become fields onthat object

It can then be decomposed into other methods on the same object that object. It can then be decomposed into other methods on the same object.

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Patterns in Software Engineering – Lecture 10 Moving Features Between Objects:

Move Method

Moving

Features Between Objects:

Move

Method

Mo e Method „ Move Method^ ^ A method is, or will be, using or used by more features of another class than theclass on which it is defined.^ ^ Create a new method with a similar body in the class it uses most. Either turnthe old method into a simple delegation, or remove it altogether. Department of Computer Engineering

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Patterns in Software Engineering – Lecture 10 Moving Features Between Objects:

Move Field

Moving

Features Between Objects:

Move

Field

„^ Move Field^ ^

A field is, or will be, used by another class more than the class on which it isdefined. Create a new field in the target class, and change all its users.

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Patterns in Software Engineering – Lecture 10 Moving Features Between Objects:

Extract Class

Moving

Features Between Objects:

Extract

Class

„^ Extract Class^ ^

You have one class doing work that should be done by two. Create a new class and move the relevant fields and methods from the old class Create a new class and move the relevant fields and methods from the old classinto the new class.

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Patterns in Software Engineering – Lecture 10 Moving Features Between Objects:

Inline Class

Moving

Features Between Objects:

Inline

Class

„^ Inline Class^ ^

A class isn't doing very much. Move all its features into another class and delete it Move all its features into another class and delete it.

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Patterns in Software Engineering – Lecture 10 Moving Features Between Objects:

Hide Delegate

Moving

Features Between Objects:

Hide

Delegate

„^ Hide Delegate

g

^ A client is calling a delegate class of an object. ^ Create methods on the server to hide the delegate. Department of Computer Engineering

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Patterns in Software Engineering – Lecture 10 Moving Features Between Objects:

Remove Middle Man

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j

„^ Remove Middle Man^ ^

A class is doing too much simple delegation. Get the client to call the delegate directly.

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Patterns in Software Engineering – Lecture 10 Moving Features Between Objects:

Introduce Method/Class

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j

„^ Introduce Foreign Method^

^

A server class you are using needs an additional method, but you can'tmodify the classmodify the class. Create a method in the client class with an instance of the server classas its first argument.

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„^ Introduce Local Extension^

^

A server class you are using needs several additional methods, but youcan't modify the class.C^ t

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^ Create a new class that contains these extra methods. Make thisextension class a subclass or a wrapper of the original.Department of Computer Engineering

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Patterns in Software Engineering – Lecture 10 Moving Features Between Objects:

Introduce Local Extension

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Patterns in Software Engineering – Lecture 10 R fReference „ Fowler, M.,

Refactoring: Improving the Design of Existing Code,

Addison-Wesley, 1999.Department of Computer Engineering

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