Refactoring Refactoring, applied - Purdue Universityprogram’s code is not structured in a...

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Refactoring

Martin Fowler (and Kent Beck, John Brant, William Opdyke, Don Roberts), Refactoring- Improving the Design of Existing Code Addison Wesley 1999

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a r e E n g i n e e r

Code, Addison Wesley, 1999.

Refactoring (noun): a change made to the internal structure of software to make it

easier to understand and

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cheaper to modify without changing its observable behavior.

Refactor (verb): to restructure software by applying a series of refactorings.

C

Refactoring, applied

Straight from the book:

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“a program to calculate and print a statement of a customer’s charges at a video store”

...price depends on how long the movie is rented and the category of the movie

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...also compute frequent renter points

C

Refactoring: Movie

Class diagram of the starting point classes.

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O b j e c t

Refactoring: Movie Classpublic class MovieMovie {

public static final int CHILDREN=2;public static final int REGULARS=0;public static final int

public void setPriceCode(int arg) {_priceCode = arg;

}

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a r e E n g

public static final int NEW_RELEASE=1;

private String _title;private int _priceCode;

public Movie(String title, int priceCode) {

_title=title;priceCode = priceCode;

public String getTitle() {return _title;

}}

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_p p}public int getPriceCode() {

return _priceCode;}

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Refactoring: Rental Classpublic class RentalRental {

private Movie _movie;private int _daysRented;


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public Rental(Movie movie, int daysRented) {

_movie = movie;_daysRented = daysRented ;

}public int getDaysRented() {

return _daysRented ;}public Movie getMovie() {

t i

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return _movie;}

}

O b j e c t

Refactoring: Customer Classpublic class CustomerCustomer {

private String _name;private Vector _rentals =new Vector();


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public Customer(String name) {_name = name;

}public void addRental(Rental arg) {

_rentals.addElement(arg);}public String getName() {

return _name;}

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O b j e c t

Refactoring: Customer Classpublic class CustomerCustomer...

public String statement() {double totalAmount = 0; O

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double totalAmount = 0;int frequentRenterPoints = 0;Enumeration rentals = _rental.elements();String result = “Rental Record for “ + getName() + “\n”;while (rentals.hasMoreElements()) {

double thisAmount = 0;Rental each = (Rental) rentals.nextElement();

// determine amounts for each lineswitch (each.getMovie().getPriceCode()) {

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switch (each.getMovie().getPriceCode()) {case Movie.REGULAR:

thisAmount += 2;if (each.getDaysRented() > 2)

thisAmount+=(each.getDaysRented()-2) * 1.5;

break;

O b j e c t

Refactoring: Customer Classpublic class CustomerCustomer

public String statement() ...

case Movie NEW RELEASE: O r i e n t e d S o f t w

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case Movie.NEW_RELEASE:thisAmount += each.getDaysRented() * 3;break;

case Movie.CHILDRENS:thisAmount += 1.5;if (each.getDaysRented() > 3)

thisAmount+=(each.getDaysRented()-3) * 1.5;

break;}

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// add frequent renter pointsfrequentRenterPoints ++;// add bonus for a two day new release rentalif ((each.getMovie().getPriceCode() == Movie.NEW_RELEASE)&&

each.getDaysRented() > 1) frequentRenterPoints++;

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O b j e c t

Refactoring: Customer Classpublic class CustomerCustomer

public String statement() ...

//show figures for this rental O r i e n t e d S o f t w

a r e E n g

// gresult += “\t” + each.getMovie().getTitle()+ “\t” +

String.valueOf(thisAmount) + “\n”;totalAmount += thisAmount;

}// add footer linesresult += “Amount owed is “+Sting.valueOf(totalAmount) + “\n”;result += “You earned “+Sting.valueOf(frequentRenterPoints)

+ “frequent renter points\n”;return result;

}

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}

C

Refactoring

Interaction diagram for the statement method.

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C

Refactoring: problem statement

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Add a htmlStatment method which returns a customer statement string containing html tags.

...and there will be some changes to the way movies are classified

affecting frequent renter points and charging

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...affecting frequent renter points and charging.

When you find you have to add a feature to a program, and the program’s code is not structured in a convenient way to add it, refactor the code.

CRefactoring: step 1

Write a test suite !

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Refactoring should not affect the outcome of tests. The test suite must exercise the published interface of the classes.

Obviously, refactoring should not affect the published interface. So, avoid publishing interfaces too early.

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f , p g f y

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Refactoring: step 2statement() is overly long, apply the Extract Method refactoring

public String statement() {double totalAmount = 0;C

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int frequentRenterPoints = 0;Enumeration rentals = _rental.elements();String result = “Rental Record for “ + getName() + “\n”;while (rentals.hasMoreElements()) {

double thisAmount = 0;Rental each = (Rental) rentals.nextElement();// determine amounts for each lineswitch (each.getMovie().getPriceCode()) {

case Movie.REGULAR:thisAmount += 2;if (each.getDaysRented() > 2)

thisAmount+=(each.getDaysRented()-2) * 1.5;b k

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break; case Movie.NEW_RELEASE:

thisAmount += each.getDaysRented() * 3; break;case Movie.CHILDRENS:

thisAmount += 1.5;if (each.getDaysRented() > 3)

thisAmount+=(each.getDaysRented()-3) * 1.5;break;

}

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Refactoring: step 2public String statement() {


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while (rentals.hasMoreElements()) {double thisAmount = 0;Rental each = (Rental) rentals.nextElement();

thisAmount = amountFor(each);// add frequent renter pointsfrequentRenterPoints ++;// add bonus for a two day new release rentalif ((each.getMovie().getPriceCode() == Movie.NEW_RELEASE)&&

each.getDaysRented() > 1) frequentRenterPoints++;//show figures for this rentalresult += “\t” + each.getMovie().getTitle()+ “\t” +

String.valueOf(thisAmount) + “\n”;

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totalAmount += thisAmount;}// add footer linesresult += “Amount owed is “+Sting.valueOf(totalAmount) + “\n”; result += “You

earned “+Sting.valueOf(frequentRenterPoints) + “frequent renter points\n”;

return result;}

C

Refactoring: step 2public public intint amountForamountFor(Rental each) {(Rental each) {

intint thisAmountthisAmount = 0;= 0;switch (each.getMovie().getPriceCode()) {

case Movie.REGULAR:CS510 S o f t w





case Movie.CHILDRENS:thisAmount += 1.5;if ( h tD R t d() 3)

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if (each.getDaysRented() > 3)thisAmount+=(each.getDaysRented()-3) * 1.5;

break;}return return thisAmountthisAmount;;

}}


TESTTESTC


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Refactoring: step 4oops, (double) oops, (double) --> (> (intint) bug!) bug!

public doubledouble amountFor(Rental each) {doubledouble thisAmount = 0;switch (each.getMovie().getPriceCode()) {C


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( g () g ()) {case Movie.REGULAR:




case Movie.CHILDRENS:thisAmount += 1.5;if ( h tD R t d() > 3)

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if (each.getDaysRented() > 3)thisAmount+=(each.getDaysRented()-3) * 1.5;

break;}return thisAmount;

}

C

Refactoring: step 5Variable names not helpful

public double amountFor(Rental each) {double thisAmount = 0;switch (each.getMovie().getPriceCode()) {

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switch (each.getMovie().getPriceCode()) {case Movie.REGULAR:




case Movie.CHILDRENS:thi A t + 1 5

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thisAmount += 1.5;if (each.getDaysRented() > 3)


}return thisAmount;

}

C

Refactoring: step 5public double amountFor(Rental aRentalaRental) {

double resultresult = 0;switch (aRentalaRental.getMovie().getPriceCode()) {

case Movie.REGULAR:CS510 S o f t w


resultresult += 2;if (aRentalaRental.getDaysRented() > 2)

resultresult +=(aRentalaRental.getDaysRented()-2) * 1.5;break;

case Movie.NEW_RELEASE:resultresult += aRentalaRental.getDaysRented() * 3;break;

case Movie.CHILDRENS:resultresult += 1.5;if ( R t lR t l tD R t d() 3)

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if (aRentalaRental.getDaysRented() > 3)resultresult +=(aRentalaRental.getDaysRented()-3) * 1.5;

break;}return resultresult ;

}


Moving amount computation (does not use info from Customer only Rental)class Customer ...public double amountFor(Rental aRentalaRental) {

double resultresult = 0;CS510 S o f t w


switch (aRentalaRental.getMovie().getPriceCode()) {case Movie.REGULAR:

resultresult += 2;if (aRentalaRental.getDaysRented() > 2)


case Movie.NEW_RELEASE:resultresult += aRentalaRental.getDaysRented() * 3;break;

case Movie.CHILDRENS:resultresult += 1 5;

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resultresult += 1.5;if (aRentalaRental.getDaysRented() > 3)


}return resultresult ;

}

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Refactoring: step 6class Rental class Rental ......public double getCharge() {

double resultresult = 0;switch (getMovie().getPriceCode()) {

case Mo ie REGULAR

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case Movie.REGULAR:resultresult += 2;

if (getDaysRented() > 2)resultresult +=(getDaysRented()-2) * 1.5;

break; case Movie.NEW_RELEASE:

resultresult += getDaysRented() * 3;break;

case Movie.CHILDRENS:

resultresult += 1.5;

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if (getDaysRented() > 3)

resultresult +=(getDaysRented()-3) * 1.5;break;

}return resultresult ;

}

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Refactoring: step 6class Customer ...class Customer ...public double amountFor(Rental aRental) {

return aRental.getChargeaRental.getCharge()();;}C


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C

Refactoring: step 7class Customer ...public String statement() {

double totalAmount = 0;int frequentRenterPoints = 0;Enumeration rentals = _rental.elements();String result = “Rental Record for “ + getName() + “\n”;

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String result = Rental Record for + getName() + \n ;while (rentals.hasMoreElements()) {

double thisAmount = 0;Rental each = (Rental) rentals.nextElement();thisAmount = amountFor(each);// add frequent renter pointsfrequentRenterPoints ++;// add bonus for a two day new release rentalif ((each.getMovie().getPriceCode() == Movie.NEW_RELEASE)&&



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return result;}


class Customer ...public String statement() {

double totalAmount = 0;int frequentRenterPoints = 0;Enumeration rentals = _rental.elements();String result = “Rental Record for “ + getName() + “\n”;

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String result = Rental Record for + getName() + \n ;while (rentals.hasMoreElements()) {

double thisAmount = 0;Rental each = (Rental) rentals.nextElement();thisAmount = each.getCharge();// add frequent renter pointsfrequentRenterPoints ++;// add bonus for a two day new release rentalif ((each.getMovie().getPriceCode() == Movie.NEW_RELEASE)&&



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return result;}

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Refactoring

State of classes after moving the charge method. amountFor has been deleted.

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C

Refactoring: step 8Replace Temp with Query (thisAmount is redundant)

class Customer ...class Customer ...public String statement() {

double totalAmount = 0;int frequentRenterPoints = 0;

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Rental each = (Rental) rentals.nextElement();// add frequent renter pointsfrequentRenterPoints ++;// add bonus for a two day new release rentalif ((each.getMovie().getPriceCode() == Movie.NEW_RELEASE)&&


)) + “\n”;

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totalAmount += each.getCharge(); String.valueOf(each.getCharge(}// add footer linesresult += “Amount owed is “+Sting.valueOf(totalAmount) + “\n”; result += “You


return result;}

C

Refactoring: step 9Extract Method (frequent renter computation)


double totalAmount = 0;int frequentRenterPoints = 0;

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Rental each = (Rental) rentals.nextElement();// add frequent renter points// add frequent renter pointsfrequentRenterPointsfrequentRenterPoints ++;++;// add bonus for a two day new release rental// add bonus for a two day new release rentalif ((if ((each.getMovieeach.getMovie().().getPriceCodegetPriceCode() == () == Movie.NEW_RELEASEMovie.NEW_RELEASE)&&)&&

each.getDaysRentedeach.getDaysRented() > 1) () > 1) frequentRenterPointsfrequentRenterPoints++;++;//show figures for this rentalresult += “\t” + each.getMovie().getTitle()+ “\t” +

String.valueOf(each.getCharge()) + “\n”;

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totalAmount += each.getCharge();}// add footer linesresult += “Amount owed is “+Sting.valueOf(totalAmount) + “\n”; result += “You


return result;}



double totalAmount = 0;int frequentRenterPoints = 0;Enumeration rentals = _rental.elements();C


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String result = “Rental Record for “ + getName() + “\n”;while (rentals.hasMoreElements()) {

Rental each = (Rental) rentals.nextElement();frequentRenterPointsfrequentRenterPoints += += each.getFrequentRenterPointseach.getFrequentRenterPoints();();

//show figures for this rentalresult += “\t” + each.getMovie().getTitle()+ “\t” +

String.valueOf(each.getCharge()) + “\n”;totalAmount += each.getCharge();

}// add footer linesresult + “Amount owed is “+Sting valueOf(totalAmount) + “\n”; result + “You

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result += “Amount owed is “+Sting.valueOf(totalAmount) + “\n”; result += “You earned “+Sting.valueOf(frequentRenterPoints)

+ “frequent renter points\n”;return result;

}

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Refactoring: step 9class Rental ...class Rental ...public int getFrequentRenterPoints() {

if ((if ((getMoviegetMovie().().getPriceCodegetPriceCode() == () == Movie.NEW_RELEASEMovie.NEW_RELEASE) ) && && getDaysRentedgetDaysRented() > 1) () > 1) C


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g yg yreturn 2;return 2;

else else return 1;return 1;

}}

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C

RefactoringClass diagram before extraction and movement of the frequent renter points calculation

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Interaction diagram before extraction and movement of the frequent renter points calculation

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C

RefactoringClass diagram after extraction and movement of the frequent renter points calculation

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Interaction diagram after extraction and movement of the frequent renter points calculation

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getFrequentRenterPoints()


Replace Temp with Query (the temporaries make the method complex and force code duplication)

class Customer ...public String statement() {C


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Rental each = (Rental) rentals.nextElement();frequentRenterPoints += each.getFrequentRenterPoints();

//show figures for this rentalresult += “\t” + each.getMovie().getTitle()+ “\t” +

String.valueOf(each.getCharge()) + “\n”;totalAmount + each getCharge();

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totalAmount += each.getCharge();}// add footer linesresult += “Amount owed is “+Sting.valueOf(totalAmount) + “\n”; result += “You


return result;}

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Refactoring: step 10class Customer ...class Customer ...public String statement() {

int frequentRenterPoints = 0;Enumeration rentals = _rental.elements();C


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String result = “Rental Record for “ + getName() + “\n”;while (rentals.hasMoreElements()) {

Rental each = (Rental) rentals.nextElement();frequentRenterPoints += each.getFrequentRenterPoints();//show figures for this rentalresult += “\t” + each.getMovie().getTitle()+ “\t” +

String.valueOf(each.getCharge()) + “\n”;}// add footer lines

lt “A t d i “ Sti l Of( tT t lChtT t lCh ()()) “\ ”

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result += “Amount owed is “+Sting.valueOf(getTotalChargegetTotalCharge()()) + “\n”;result += “You earned

“+Sting.valueOf(frequentRenterPoints)+“frequent renter points\n”;

return result;}

C

Refactoring: step 10class Customer ...class Customer ...private double getTotalCharge() {

double result = 0;Enumeration rentals = rentals.elements();C


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_while (rentals.hasMoreElements()) {

Rental each = (Rental) rentals.nextElement();result += each.getCharge();

}return result;

}

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C

Refactoring: step 11Replace Temp with Query


int frequentRenterPoints = 0;

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int frequentRenterPoints 0;Enumeration rentals = _rental.elements();String result = “Rental Record for “ + getName() + “\n”;while (rentals.hasMoreElements()) {

Rental each = (Rental) rentals.nextElement();frequentRenterPoints += each.getFrequentRenterPoints();//show figures for this rentalresult += “\t” + each.getMovie().getTitle()+ “\t” +

String.valueOf(each.getCharge()) + “\n”;}// dd f t li

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// add footer linesresult += “Amount owed is “+Sting.valueOf(getTotalCharge()) + “\n”;result += “You earned “+Sting.valueOf(frequentRenterPoints)+

“frequent renter points\n”;return result;

}


Replace Temp with Queryclass Customer ...class Customer ...public String statement() {

Enumeration rentals = rental.elements();CS510 S o f t w


u e at o e ta s _ e ta .e e e ts();String result = “Rental Record for “ + getName() + “\n”;while (rentals.hasMoreElements()) {

Rental each = (Rental) rentals.nextElement();//show figures for this rentalresult += “\t” + each.getMovie().getTitle()+ “\t” +

String.valueOf(each.getCharge()) + “\n”;}// add footer linesresult += “Amount owed is “+Sting.valueOf(getTotalCharge()) + “\n”;

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g (g g ())

result += “You earned “+Sting.valueOf(getFrequentRenterPointsgetFrequentRenterPoints()())+“frequent renter points\n”;

return result;}

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Refactoring: step 11class Customer ...class Customer ...

private double getFrequentRenterPoints() {double result = 0;Enumeration rentals = rentals.elements();C


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_while (rentals.hasMoreElements()) {

Rental each = (Rental) rentals.nextElement();result += each.getFrequentRenterPoints();

}return result;

}

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C

RefactoringClass diagram before extraction of the totals

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Interaction diagram before extraction of the totals

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getFrequentRenterPoints()

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RefactoringClass diagram after extraction of the totals

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Interaction diagram after extraction of the totals

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CRefactoring

RemarksMost refactoring reduce code size, but this is not necessarily the case The point is to make code easier to modify and more

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the case. The point is to make code easier to modify and more readable.Performance gets a hit by running the same loop three times, or does it? Profile the program and find the answer.

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Software extensionThe requested method can be added with minimal code duplication

l C t

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class Customer ...public String htmlStatement() {

Enumeration rentals = _rental.elements();String result = “<H1>Rental Record for “ + getName() + “</H1>\n”;while (rentals.hasMoreElements()) {

Rental each = (Rental) rentals.nextElement();//show figures for this rentalresult += each.getMovie().getTitle()+ “: ” +

String.valueOf(each.getCharge()) + “ \n”;}// add footer lines

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// add footer linesresult += “Amount owed is “+Sting.valueOf(getTotalCharge()) +

“\n”; result += “You earned “+Sting.valueOf(getFrequentRenterPointsgetFrequentRenterPoints()())+

“ frequent renter points\n”;return result;

}

C

New functionality

Getting ready to change the classification of the movies in the store. P h l f h d f

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Perhaps new classification, perhaps modification to existing.Charging and frequent renting will be affected.

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C

Refactoring: step 12Replacing conditional logic on Price Code with polymorphism

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Move getChargeclass Rental ...class Rental ...public double getCharge() {

double result = 0;CS510 S o f t w


switch (getMovie().getPriceCode()) {case Movie.REGULAR:

result += 2;if (getDaysRented() > 2)

result +=(getDaysRented()-2) * 1.5;break;

case Movie.NEW_RELEASE:result += getDaysRented() * 3;break;

case Movie.CHILDRENS:result += 1 5;

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result += 1.5;if (getDaysRented() > 3)


}return result ;

}

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Refactoring: step 12class Movie ...class Movie ...public double getCharge(int daysRented) {

double result = 0;switch (getPriceCode()) {

case REGULAR

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case REGULAR:result += 2;if (daysRented > 2)

result +=(daysRented-2) * 1.5;break;

case NEW_RELEASE:result += daysRented * 3;break;

case CHILDRENS:result += 1.5;

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if (daysRented > 3)result +=(daysRented-3) * 1.5;

break;}return result ;

}

C

Refactoring: step 12class Rental ...class Rental ...public double getCharge() {

return _movie.getCharge(_daysRented);}C


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C

Refactoring: step 13Move getFrequentRenterPoints()

class Rental ...class Rental ...public int getFrequentRenterPoints() {

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public int getFrequentRenterPoints() {if ((getMovie().getPriceCode() == Movie.NEW_RELEASE)&& getDaysRented() > 1)

return 2;else

return 1;}

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class Movie ...public int getFrequentRenterPointsgetFrequentRenterPoints((intint daysRenteddaysRented) ) {

if ((getPriceCode() == Movie.NEW_RELEASE) && daysRented > 1) return 2;C


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else return 1;

}

class Rental ...public int getFrequentRenterPoints() {

return _movie.getFrequentRenterPoints(_daysRented);

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}

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Refactoring

Class diagram before moving methods to movie

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Class diagram after moving methods to movie

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Refactoring

Inheritance

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C

RefactoringInheritance

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Replace Type Code with State/StrategyC


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class Movie ...class Movie ...public Movie(String name, int priceCode) {

_name = name;_priceCode = priceCode;

}

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Refactoring: step 14

class Movie ...class Movie ...public Movie(String name, int priceCode) {

_name = name;CS510 S o f t w


setPriceCode(priceCode);setPriceCode(priceCode);}

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Refactoring: step 14abstract class Price {

abstract int getPriceCode();}

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class ChildrenPrice extends Price {int getPriceCode(){

return MOVIE.CHILDREN;}

}class NewReleasePrice extends Price {

int getPriceCode(){return MOVIE.NEW_RELEASE;

}}

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}class RegularPrice extends Price {

int getPriceCode(){return MOVIE.REGULAR;

}}

C

Refactoring: step 15class Movie ...class Movie ...

public int getPriceCode() {return priceCode;C


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_p}public void setPriceCode(int arg) {

_priceCode = arg;}private int _priceCode;

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class Movie ...class Movie ...public int getPriceCode() {

return _return _price.getPriceCodeprice.getPriceCode;;}p blic oid setPriceCode(int arg) {

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public void setPriceCode(int arg) {switch (switch (argarg) {) {

case REGULAR:case REGULAR:_price = new _price = new RegularPriceRegularPrice();();break;break;

case CHILDREN:case CHILDREN:_price = new _price = new ChildrenPriceChildrenPrice();();break;break;

case NEW_RELEASE:case NEW_RELEASE:_price = new _price = new NewReleasePriceNewReleasePrice();();

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break;break;default: default: throw new throw new IllegalArgumentExceptionIllegalArgumentException(“Incorrect Price Code”);(“Incorrect Price Code”);

}}}private Price _price;private Price _price;

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Refactoring: step 16Move Method

class Movie ...class Movie ...public double getCharge(int daysRented) {



switch (getPriceCode()) {case REGULAR:



case NEW_RELEASE:result += getDaysRented() * 3;break;

case CHILDRENS:result += 1 5;

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result + 1.5;if (getDaysRented() > 3)


}return result ;

}

C

Refactoring: step 16class Movie ...class Movie ...public double getCharge(int daysRented) {

return __price.getChargeprice.getCharge((daysRenteddaysRented));}C


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C

Refactoring: step 16Replace Conditional with Polymorphism

class Price ...class Price ...double getCharge(int daysRented) {



switch (getPriceCode()) {case MOVIE.REGULAR:



case MOVIE.NEW_RELEASE:result += getDaysRented() * 3;break;

case MOVIE.CHILDRENS:result += 1 5;

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result += 1.5;if (getDaysRented() > 3)


}return result ;

}


class RegularPrice ...class RegularPrice ...double getCharge(int daysRented) {

double result = 2;if (getDaysRented() > 2)res lt + (getDa sRented() 2) * 1 5

CS510 S o f t w


result +=(getDaysRented()-2) * 1.5;return result;

}class NewReleasePrice ...class NewReleasePrice ...double getCharge(int daysRented) {

return daysRented * 3;}class ChildrenPrice ...class ChildrenPrice ...double getCharge(int daysRented) {

double result = 1.5;

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if (getDaysRented() > 3)result +=(getDaysRented()-3) * 1.5;

return result ;}class Price...class Price...

abstract double getCharge(int daysRented);

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C

Refactoring: step 17Replace Conditional with Polymorphism

class Rental ...class Rental ...int getFrequentRenterPoints(int daysRented) {

CS510 S o f t w


int getFrequentRenterPoints(int daysRented) {if ((getPriceCode() == Movie.NEW_RELEASE) && daysRented > 1)

return 2;else

return 1;}

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C

Refactoring: step 17class Movie ...class Movie ...int getFrequentRenterPoints(int daysRented) {

return _price.getFrequentRenterPoints(daysRented);}C


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class Price...class Price...int getFrequentRenterPoints(int daysRented) {

return 1;}

class class NewReleasePriceNewReleasePrice....int getFrequentRenterPoints(int daysRented) {

return (daysRented > 1) ? 2:1;

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}

C

Refactoring Principles

Why do we Why do we refactorrefactor??To improve the design of softwareTo make software easier to understandC


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To help you find bugsTo make you program faster

When should we When should we refactorrefactor??1. Refactor when you add functionality2. Refactor when you need to fix a bug3. Refactor as you do code reviews– Refactor when the code starts to smell.

What about performance?What about performance?

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What about performance?What about performance?Worry about performance only when you have identified a performance problem

CBad Smells in Code

If it stinks, change it.--Grandma Beck on child rearing

CS510 S o f t w


Duplicated Code (stench 10)

If the same code structure is repeated

Extract Method- gather duplicated codePull Up Field - move to a common parentF T l t M th d th si il ts l i h l s

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Form Template Method - gather similar parts, leaving holesSubstitute Algorithm - choose the clearer algorithmExtract class - for unrelated classes, create a new class with functionality

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C

Bad Smells in Code

Long Method(stench 7)

CS510 S o f t w


If the body of a method is over a page (choose your page size)

Extract Method- extract related behaviorReplace Temp with Query - remove temporaries when they obscure meaningIntroduce Parameter Object - slim down parameter lists by

ki h i bj

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making them into objectsReplace Method with Method Object - still too many parametersDecompose Conditionals - conditional and loops can be moved to their own methods

C

Bad Smells in Code

Large Class (stench 7)

If l h ith t i bl t th d

CS510 S o f t w


If a class has either too many variables or too many methods

Extract Class - to bundle variables/methods

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C

Bad Smells in Code

Divergent Change (stench 5)

If fi d lf t dl h i th l th

CS510 S o f t w


If you find yourself repeatedly changing the same class thenthere is probably something wrong with it

Extract Class - group functionality commonly changed into a class

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CBad Smells in Code

Shotgun Surgery (stench 5)

If fi d lf ki l t f ll h f h

CS510 S o f t w


If you find yourself making a lot of small changes for each desired

change

Move Method/Field - pull all the changes into a single classInline Class - group a bunch of behaviors together

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C

Bad Smells in Code

Feature Envy(stench 6)

CS510 S o f t w


If a method seems more interested in a class other than the class it

actually is in

Move Method - move the method to the desired classExtract Method - if only part of the method shows the

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symptoms

C

Bad Smells in Code

Data Clumps (stench 4)

D t it th t f tl t th i th d i t

CS510 S o f t w


Data items that are frequently together in method signatures and

classes belong to a class of their own

Extract Class - turn related fields into a classIntroduce Parameter Object - for method signatures

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C

Bad Smells in Code

Primitive Obsession (stench 3)

CS510 S o f t w


Primitive types inhibit change

Replace Data Value with Object - on individual data valuesMove Method/Field - pull all the changes into a single classIntroduce Parameter Object - for signaturesReplace Array with Object - to get rid of arrays

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CBad Smells in Code

Switch Statements(stench 5)

CS510 S o f t w


Switch statements lead to duplication and inhibit change

Extract method - to remove the switchMove method - to get the method where polymorphism can applyReplace Type Code with State/Strategy - set up inheritance

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Replace Conditional with Polymorphism - get rid of the switch

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C

Bad Smells in Code

Parallel Inheritance Hierarchies (stench 6)

If h k b l i f th hi h

CS510 S o f t w


If when ever you make a subclass in one corner of the hierarchy, you must create another subclass in another corner

Move Method/Field - get one hierarchy to refer to the other

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C

Bad Smells in Code

Lazy Class (stench 4)

If l ( ft f t i ) d t d h li i t it

CS510 S o f t w


If a class (e.g. after refactoring) does not do much, eliminate it.

Collapse Hierarchy- for subclassesInline Class - remove a single class

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C

Bad Smells in Code

Speculative Generality(stench 4)

CS510 S o f t w


If a class has features that are only used in test cases, remove them.

Collapse Hierarchy- for useless abstract classesInline Class - for useless delegationRename Method - methods with odd abstract names should be b h d h

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brought down to earth

CBad Smells in Code

Temporary Field (stench 3)

If l h fi ld th t l t i i l t t

CS510 S o f t w


If a class has fields that are only set in special cases, extract them

Extract Class- for the special fields

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C

Bad Smells in Code

Message Chains (stench 3)

L h i f t t t l b ittl

CS510 S o f t w


Long chains of messages to get to a value are brittle as any change

in the intermittent structure will break the code

Hide Delegate - remove one link in a chainExtract Method - change the behavior to avoid chains

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C

Bad Smells in Code

Middle Man (stench 3)

A i t di bj t i d t ft t t t

CS510 S o f t w


An intermediary object is used too often to get at encapsulated values

Remove Middle Man - to talk directly to the targetReplace Delegation with Inheritance - turns the middle man into a subclass of the real object

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C

Bad Smells in Code

Inappropriate Intimacy (stench 5)

Cl t i ti t d d t h ti d l i i

CS510 S o f t w


Classes are too intimate and spend too much time delving in each other’s private parts

Move Method/Field - to separate pieces in order to reduce intimacyExtract Class - make a common class of shared behavior/dataReplace Inheritance with Delegation - when a subclass is

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Replace Inheritance with Delegation when a subclass is getting too cozy

CBad Smells in Code

Comments (stench 2)

C t ft i f l d id

CS510 S o f t w


Comments are often a sign of unclear code... consider refactoring

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Refactoring Refactoring, applied - Purdue Universityprogram’s code is not structured in a...

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