meljun cortes java refactoring

8/10/2019 MELJUN CORTES JAVA Refactoring

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Refactoring

Improving the Design of Existing Code

MELJUN CORTES MBA MPA BSCS


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Topic Coverage

Background of refactoring

What is Refactoring?

Where it came from Principles in Refactoring

The Two Hats Metaphor

Why and When

Refactoring and Design

Refactoring and Performance


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Topic Coverage (cont.)

Bad Smells

What is code smell?

Types of code smells Types of Refactoring

Types of refactoring.


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Background of

Refactoring

What is Refacto r ing?

Where it came from


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What is Refactoring?

Disciplined way to code

Over time code will be modified

Changing code in small steps

Verify no change in external behavior by

Testing

Formal code analysis by tool

Refactoring is the process of changing a software system

in such a way that it does not alter the external behavior of

the code yet improves its internal structure.


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Where Refactoring Came

From?

Ward Cunningham and Kent Beck

Smalltalk style

Ralph Johnson at University of Illinois at

Urbana-Champaign Bill Opdykes Thesis

ftp://st.cs.uiuc.edu/pub/papers/refactoring/opdyke-thesis.ps.Z

John Brant and Don Roberts: TheRefactoring Browser


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Principles in

Refactoring

The Two Hats Metapho r

Why and When

Refactor ing and Design

Refacto r ing and Perform ance


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The Two Hats Metaphor

Adding Function

Add new capabilities

to the system

Adds new tests

Get the test working

Refactoring

Does not add any

new features

Does not add tests

(but may change some)

Restructure the code

to remove redundancy

Swap frequently between the hats,

bu t only w ear on e at a time


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Why Refactor?

To improve the software design

Combats bit rot

Makes the program easier to change

To make the software easier to understand Write for people, not the compiler

Understand unfamiliar code

To help find bugs

Refactor while debugging to clarify the code

Refactoring helps you program faster.


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When to Refactor?

To add new functionality

Refactor existing code until youunderstand it

Refactor the design to make it easy toadd

To find bugs

Refactor to understand the code

For code reviews Immediate effect of code review

Allows for higher level suggestions

Dont set aside time for refactoring,

inc lude i t in you r norm al act iv i t ies


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Refactoring and Design

Special role as a complement to

design.

Refactoring can be an alternative to

upfront design

Refactoring can lead to simpler

design without sacrificing flexibility


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Refactoring and

Performance

Refactoring make software go more

slowly Refactoring makes the software more

amenable to performance tuning

Well refactored program gives you time to

spend on performance tuning Well refactored program you have finer

granularity for you performance analysis

The best way to optimize performance is to first write

a well factored program, then optimize it.


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Types of Refactoring


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Extract Method

You have a code fragment that can be grouped togetherTurn the fragment into a method whose name explains the

Purpose of the method.

void printOwing(double amount){printBanner();

//printDetailsSystem.out.println(name:+ _name);System.out.println(amount:+ amount);

}

void printOwing(double amount){

printBanner();printDetails(amount);

}

void printDetails(double amount){

System.out.println(name:+ _name);

System.out.println(amount:+ amount);}


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Inline Method

A methods body is just as clear as its name

Put the methods body in the body of its callers and remove the method

int getRating(){return (moreThanFIveLateDeliveries()) ? 2 : 1;}

boolean moreThanFIveLateDeliveries(){return _numberOfLateDeliveries > 5;

}

int getRating(){

return (_numberOfLateDeliveries > 5) ? 2 : 1;}


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Inline Temp

You have a temp that assigned to once with a simple expression,

and the temp is getting in the way of other refactorings.

Replace all references to that temp with the expression

double basePrice anOrder.basePrice();return (basePrice > 1000)

return (anOrder.basePrice() > 1000)


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Replace Temp with Query

You are using a temporary variable to hold the

result of an expression

Extract the expression into a method. Replace all references to the temp

with the expression. The new method can then be

used in other methods.double basePrice = _quantity * _itemPrice;if ( basePrice > 1000)

return basePrice * 0.95;else

return basePrice * 0.98;

if (basePrice() > 1000)return basePrice() * 0.95;

elsereturn basePrice() * 0.98;

...double basePrice(){

return _quantity * _itemPrice;}


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Introduce Explaining

Variable

You have a complicated expression

Put the result of the expression, or parts of the expression, in a

temporary variable with a name that explains the purpose.

if ( (platform.toUpperCase().indexOf(MAC) > -1) &&(browser.toUpperCase().indexOf(IE) > -1 &&

wasInitialized() && resize > 0 ) {

// do something ...}

final boolean isMacOs = platform.toUpperCase().indexOf(MAC) > -1;final boolean isIEBrowser = platform.toUpperCase().indexOf(IE) > -1;

final boolean wasResized = resize > 0;

if (isMacOs && isIEBrowser && wasInitialized() && wasResized) {

//do something}


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Move Method

A method is, or will be, using or used by more

features of another class that the class on which it

is defined

Create a new method with a similar body in the class it uses most.

Either turn the old method into a simple delegation, or

remove it altogether.

Class 1

aMethod()

Class 2

Class 1

Class 2

aMethod()


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Move Field

A field is, or will be, used by another class more than the class

on which it is defined.

Create a new field in the target class, and change all its users.

Class 1

aField

Class 2

Class 1

Class 2

aField


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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 into the new class

Person

nameofficeAreaCode

officeNumber

getTelephoneNumber()

Person

name


Telephone Number

areaCode

number


officeTelephone

1


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Inline Class

A class isnt doing very much

Move all its features into another class and delete it.

Person

nameofficeAreaCode

officeNumber


Person

name


Telephone Number

areaCode

number


officeTelephone

1


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Pull Up Field

Two subclasses have the same field

Move the field to the superclass.

Employee

Salesman

name

Engineer

name

Employee

name

EngineerSalesman


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Pull Up Method

You have methods with identical results on subclass

Move them to the superclass

Employee

Salesman

getName()

Engineer

getName()

Salesman

Employee

getName()

Engineer


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Pull Up Constructor Body

You have constructor on subclasses with mostly

Identical bodies.

Create a superclass constructor; call this from the

subclass methods

class Manager extends Employee ...public Manager (String name, String id, int grade) {

_name = name;_id = id;_grade = grade;

}

public Manager (String name, String id, int grade) {super(name, id);

_grade = grade;}


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Push Down Method

Behavior on a superclass is relevant only for

some of its subclasses

Move it to those subclasses

Employee

Salesman

getQuota()

EngineerSalesman

Employee

getQuota()

Engineer


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Push Down Field

Two subclasses have the same field

Move the field to the superclass.

Employee

Salesman

quota

Engineer

Employee

quota

EngineerSalesman


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Rename Method

The name of a method does not reveal its purpose.

Change the name of the method

Customer

getinvcdtlmt()

Customer

getInvoiceCreditLimit()


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Add Parameter

A method needs more information from its caller.

Add a parameter for an object that can pass on

this information.

Customer

getContact()

Customer

getContact(:Date)


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Remove Parameter

A parameter is no longer used by the method body.

Remove it

Customer

getContact()

Customer

getContact(:Date)

meljun cortes java refactoring

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