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

Part 1

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Part^

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: 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

g

4.^ Long Parameter ListDi

t Ch^

Wh^

l^ i^

l^ h^

d i^ diff

t

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 (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

p^

g^

g^ g^

p^ p^

y

„^ Moving Features Between Objects:

Reassigning responsibilities

O^

i i^

D t^

M ki^

d t^

i^ t^

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:

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 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:

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

g^

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 Local Extension

g^

j

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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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