Refactoring Example

Refactoring CMPUT 301: Lecture 14 Example: Refactoring a program to calculate and print a statement of a customer s charges at a video store Lecturer: Sherif Ghali Department of Computing Science University of Alberta Notes credits: Ken Wong, Sherif Ghali (Some slides removed by M. Hicks) 2 1

Class Diagram Movie public class Movie { public static final int CHILDRENS = 2; public static final int REGULAR = 0; Customer Rental public static final int NEW_RELEASE = 1; * -daysRented : int private String _title; private int _priceCode; +statement() +getDaysRented (): int public Movie( String title, int priceCode ) { _title = title; * _priceCode = priceCode; } 1 public int getPriceCode() { return _priceCode; Movie } public void setPriceCode( int arg ) { -priceCode : int _priceCode = arg; } +getPriceCode (): int public String getTitle() { return _title; } } 3 4 2

Rental Customer class Rental { class Customer { private Movie _movie; private String _name; private int _daysRented; private Vector _rentals = new Vector(); public Customer( String name ) { public Rental( Movie movie, int daysRented ) { _name = name; _movie = movie; } _daysRented = daysRented; public void addRental( Rental arg ) { } _rentals.addElement( arg ); public int getDaysRented() { } return _daysRented; public String getName() { } return _name; } public Movie getMovie() { return _movie; } } } 5 6 3

Customer::statement() Customer::statement() public String statement() { double totalAmount = 0; // add frequent renter points int frequentRenterPoints = 0; frequentRenterPoints++; Enumeration rentals = _rentals.elements(); // add bonus for a two day new release rental String result = Rental Record for + getName() + n ; if ((each.getMovie().getPriceCode() == Movie.NEW_RELEASE) && each.getDaysRented() > 1) frequentRenterPoints++; while (rentals.hasMoreElements()) { double thisAmount = 0; // show figures for this rental Rental each = (Rental)rentals.nextElement(); result += t + each.getMovie().getTitle() + t + // determine amounts for each line String.valueOf( thisAmount ) + n ; switch (each.getMovie().getPriceCode()) { totalAmount += thisAmount; case Movie.REGULAR: } thisAmount += 2; if (each.getDaysRented() > 2) // add footer lines thisAmount += (each.getDaysRented() - 2) * 1.5; result += Amount owed is + String.valueOf( totalAmount ) + n ; break; result += You earned + String.valueOf( frequentRenterPoints ) + case Movie.NEW_RELEASE: frequent renter points ; thisAmount += each.getDaysRented() * 3; break; return result; case Movie.CHILDRENS: } thisAmount += 1.5; } if (each.getDaysRented() > 3) thisAmount += (each.getDaysRented() - 3) * 1.5; break; } 7 8 4

Refactoring Refactoring Something is rotten in the state of :Customer :Rental :Movie Denmark statement() * [for all rentals] What is it? getMovie () getPriceCode () getDaysRented () 9 10 5

Refactoring Refactoring Issues: Idea: not object-oriented If the code is not structured conveniently to statement( ) routine does too much add a feature, first refactor the program to Customer class is a blob make it easy to add the feature, then add the feature. potentially difficult to make changes e.g., HTML output e.g., new charging rules 11 12 6

Refactoring Refactoring First step: Decompose statement() method: Build self-checking tests. Extract logical chunk of code as a new method. Apply Extract Method. 13 14 7

class Customer { public String statement() { Refactoring double totalAmount = 0; int frequentRenterPoints = 0; class Customer { Enumeration rentals = _rentals.elements(); String result = Rental Record for + getName() + n ; public String statement() { while (rentals.hasMoreElements()) { double totalAmount = 0; double thisAmount = 0; int frequentRenterPoints = 0; Rental each = (Rental)rentals.nextElement(); Enumeration rentals = _rentals.elements(); String result = Rental Record for + getName() + n ; // determine amounts for each line switch (each.getMovie().getPriceCode()) { while (rentals.hasMoreElements()) { case Movie.REGULAR: double thisAmount = 0; thisAmount += 2; Rental each = (Rental)rentals.nextElement(); if (each.getDaysRented() > 2) thisAmount += (each.getDaysRented() - 2) * 1.5; break; thisAmount = amountFor( each ); 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; } 15 16 8

Refactoring Refactoring class Customer { Compile and test! private double amountFor( Rental each ) { double thisAmount = 0; small steps switch (each.getMovie().getPriceCode()) { case Movie.REGULAR: thisAmount += 2; if (each.getDaysRented() > 2) thisAmount += (each.getDaysRented() - 2) * 1.5; break; What do we do next? 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; } return thisAmount; } } 17 18 9

Refactoring Refactoring class Customer { Rename variables in amountFor(): private double amountFor( Rental each ) { double thisAmount = 0; Enhance readability. switch (each.getMovie().getPriceCode()) { case Movie.REGULAR: thisAmount += 2; if (each.getDaysRented() > 2) thisAmount += (each.getDaysRented() - 2) * 1.5; 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; } return thisAmount; } } 19 20 10

Refactoring Refactoring class Customer { private double amountFor( Rental aRental ) { Compile and test. double result = 0; switch (aRental.getMovie().getPriceCode()) { case Movie.REGULAR: result += 2; if (aRental.getDaysRented() > 2) result += (aRental.getDaysRented() - 2) * 1.5; What do we do next? break; case Movie.NEW_RELEASE: result += aRental.getDaysRented() * 3; break; case Movie.CHILDRENS: result += 1.5; if (aRental.getDaysRented() > 3) result += (aRental.getDaysRented() - 3) * 1.5; break; } return result; } } 21 22 11

Refactoring Refactoring Move amountFor() to Rental class: class Customer { private double amountFor( Rental aRental ) { Method uses rental information, but not double result = 0; switch (aRental.getMovie().getPriceCode()) { customer information. case Movie.REGULAR: result += 2; if (aRental.getDaysRented() > 2) Move method to the right class. result += (aRental.getDaysRented() - 2) * 1.5; break; case Movie.NEW_RELEASE: Apply Move Method. result += aRental.getDaysRented() * 3; break; case Movie.CHILDRENS: result += 1.5; if (aRental.getDaysRented() > 3) result += (aRental.getDaysRented() - 3) * 1.5; break; } return result; } } 23 24 12

Refactoring Refactoring class Customer { class Rental { private double amountFor( Rental aRental ) { double getCharge() { double result = 0; return aRental.getCharge(); 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; if (getDaysRented() > 3) result += (getDaysRented() - 3) * 1.5; break; } return result; } } 25 26 13

Refactoring Refactoring Compile and test. Replace references to amountFor() with getCharge(): Adjust references to old method to use new method. Remove old method. 27 28 14

Refactoring Refactoring class Customer { class Customer { public String statement() { public String statement() { double totalAmount = 0; double totalAmount = 0; int frequentRenterPoints = 0; int frequentRenterPoints = 0; Enumeration rentals = _rentals.elements(); Enumeration rentals = _rentals.elements(); String result = Rental Record for + getName() + n ; String result = Rental Record for + getName() + n ; while (rentals.hasMoreElements()) { while (rentals.hasMoreElements()) { double thisAmount = 0; double thisAmount = 0; Rental each = (Rental)rentals.nextElement(); Rental each = (Rental)rentals.nextElement(); thisAmount = amountFor( each ); thisAmount = each.getCharge(); 29 30 15

Refactoring Refactoring Compile and test. Eliminate thisAmount temporary in statement(): Replace redundant temporary variable with query. Apply Replace Temp with Query. 31 32 16

Refactoring Refactoring class Customer { class Customer { public String statement() { double totalAmount = 0; public String statement() { int frequentRenterPoints = 0; double totalAmount = 0; Enumeration rentals = _rentals.elements(); int frequentRenterPoints = 0; String result = Rental Record for + getName() + n ; Enumeration rentals = _rentals.elements(); String result = Rental Record for + getName() + n ; while (rentals.hasMoreElements()) { double thisAmount = 0; while (rentals.hasMoreElements()) { Rental each = (Rental)rentals.nextElement(); Rental each = (Rental)rentals.nextElement(); thisAmount = each.getCharge(); // add frequent renter points frequentRenterPoints++; // add frequent renter points // add bonus for a two day new release rental frequentRenterPoints++; if ((each.getMovie().getPriceCode() == Movie.NEW_RELEASE) && // add bonus for a two day new release rental each.getDaysRented() > 1) frequentRenterPoints++; if ((each.getMovie().getPriceCode() == Movie.NEW_RELEASE) && each.getDaysRented() > 1) frequentRenterPoints++; // show figures for this rental result += t + each.getMovie().getTitle() + t + // show figures for this rental String.valueOf( each.getCharge() ) + n ; result += t + each.getMovie().getTitle() + t + totalAmount += each.getCharge(); String.valueOf( thisAmount ) + n ; } totalAmount += thisAmount; } 33 34 17

Refactoring Refactoring class Customer { Extract frequent renter points logic: public String statement() { double totalAmount = 0; Applicable rules belong to the rental, not int frequentRenterPoints = 0; Enumeration rentals = _rentals.elements(); the customer. String result = Rental Record for + getName() + n ; while (rentals.hasMoreElements()) { Apply Extract Method and Move Method. Rental each = (Rental)rentals.nextElement(); // add frequent renter points frequentRenterPoints++; // add bonus for a two day new release rental if ((each.getMovie().getPriceCode() == Movie.NEW_RELEASE) && each.getDaysRented() > 1) frequentRenterPoints++; // show figures for this rental result += t + each.getMovie().getTitle() + t + String.valueOf( each.getCharge() ) + n ; totalAmount += each.getCharge(); } 35 36 18

Refactoring Refactoring class Customer { class Rental { public String statement() { double totalAmount = 0; int getFrequentRenterPoints() { int frequentRenterPoints = 0; if ((getMovie().getPriceCode() == Movie.NEW_RELEASE) && Enumeration rentals = _rentals.elements(); getDaysRented() > 1) String result = Rental Record for + getName() + n ; return 2; else while (rentals.hasMoreElements()) { return 1; Rental each = (Rental)rentals.nextElement(); } // add frequent renter points } frequentRenterPoints += each.getFrequentRenterPoints(); // show figures for this rental result += t + each.getMovie().getTitle() + t + String.valueOf( each.getCharge() ) + n ; totalAmount += each.getCharge(); } 37 38 19

Refactoring Refactoring class Customer { public String statement() { double totalAmount = 0; Eliminate totalAmount temporary: int frequentRenterPoints = 0; Enumeration rentals = _rentals.elements(); String result = Rental Record for + getName() + n ; Apply Replace Temp with Query. while (rentals.hasMoreElements()) { Rental each = (Rental)rentals.nextElement(); // add frequent renter points frequentRenterPoints += each.getFrequentRenterPoints(); // show figures for this rental result += t + each.getMovie().getTitle() + t + String.valueOf( each.getCharge() ) + n ; totalAmount += each.getCharge(); } // add footer lines result += Amount owed is + String.valueOf( totalAmount ) + n ; result += You earned + String.valueOf( frequentRenterPoints ) + frequent renter points ; return result; } } 39 40 20

Refactoring Refactoring class Customer { public String statement() { class Customer { int frequentRenterPoints = 0; Enumeration rentals = _rentals.elements(); String result = Rental Record for + getName() + n ; private double getTotalCharge() { double result = 0; while (rentals.hasMoreElements()) { Enumeration rentals = _rentals.elements(); Rental each = (Rental)rentals.nextElement(); while (rentals.hasMoreElements()) { // add frequent renter points Rental each = (Rental)rentals.nextElement(); frequentRenterPoints += each.getFrequentRenterPoints(); result += each.getCharge(); // show figures for this rental result += t + each.getMovie().getTitle() + t + } String.valueOf( each.getCharge() ) + n ; return result; } } // add footer lines } result += Amount owed is + String.valueOf( getTotalCharge() ) + n ; result += You earned + String.valueOf( frequentRenterPoints ) + frequent renter points ; return result; } } 41 42 21

Refactoring Refactoring class Customer { public String statement() { Eliminate frequentRenterPoints int frequentRenterPoints = 0; Enumeration rentals = _rentals.elements(); String result = Rental Record for + getName() + n ; temporary: while (rentals.hasMoreElements()) { Apply Replace Temp with Query. Rental each = (Rental)rentals.nextElement(); // add frequent renter points frequentRenterPoints += each.getFrequentRenterPoints(); // show figures for this rental result += t + each.getMovie().getTitle() + t + String.valueOf( each.getCharge() ) + n ; } // add footer lines result += Amount owed is + String.valueOf( getTotalCharge() ) + n ; result += You earned + String.valueOf( frequentRenterPoints ) + frequent renter points ; return result; } } 43 44 22

Refactoring Refactoring class Customer { class Customer { public String statement() { Enumeration rentals = _rentals.elements(); private int getTotalFrequentRenterPoints() { String result = Rental Record for + getName() + n ; int result = 0; Enumeration rentals = _rentals.elements(); while (rentals.hasMoreElements()) { Rental each = (Rental)rentals.nextElement(); while (rentals.hasMoreElements()) { Rental each = (Rental)rentals.nextElement(); // show figures for this rental result += t + each.getMovie().getTitle() + t + result += each.getFrequentRenterPoints(); String.valueOf( each.getCharge() ) + n ; } } return result; } // add footer lines result += Amount owed is + String.valueOf( getTotalCharge() ) + n ; } result += You earned + String.valueOf( getTotalFrequentRenterPoints() ) + frequent renter points ; return result; } } 45 46 23

Refactoring Refactoring Customer Rental :Customer :Rental :Movie * -daysRented : int statement() +statement() +getDaysRented (): int -getTotalCharge (): double +getCharge (): double getTotalCharge () -getTotalFrequentRenterPoints (): int +getFrequentRenterPoints (): int * [for all rentals] getCharge () getPriceCode () * 1 getTotalFrequentRenterPoints () Movie * [for all rentals] -priceCode : int getFrequentRenterPoints () getPriceCode () +getPriceCode (): int 47 48 24

Refactoring Customer Rental * -daysRented : int Issues: +statement() +getDaysRented ():int -getTotalChargedouble (): +getCharge double (): more code -getTotalFrequentRenterPoints ():int +getFrequentRenterPoints ():int slower performance? * 1 Movie -priceCode : int +getPriceCode ():int 49 50 25

Refactoring Refactoring New feature (HTML output): More needs: class Customer { public String htmlStatement() { Enumeration rentals = _rentals.elements(); new classifications of movies String result = <H1>Rental Record for + getName() + </H1>n ; while (rentals.hasMoreElements()) { Rental each = (Rental)rentals.nextElement(); // show figures for this rental result += each.getMovie().getTitle() + : + String.valueOf( each.getCharge() ) + <BR>n ; } // add footer lines result += <P>Amount owed is + String.valueOf( getTotalCharge() ) + </P>n ; result += <P>You earned + String.valueOf( getTotalFrequentRenterPoints() ) + frequent renter points</P> ; return result; } } 51 52 26

Refactoring Refactoring class Rental { double getCharge() { Replace conditional logic on price code double result = 0; switch (getMovie().getPriceCode()) { with polymorphism: case Movie.REGULAR: result += 2; if (getDaysRented() > 2) Rental logic should not depend on specific result += (getDaysRented() - 2) * 1.5; break; movie types. case Movie.NEW_RELEASE: result += getDaysRented() * 3; break; It is generally bad design to do a switch case Movie.CHILDRENS: result += 1.5; on an another object s attribute. if (getDaysRented() > 3) result += (getDaysRented() - 3) * 1.5; break; } return result; } } 53 54 27

Refactoring Refactoring class Movie { class Rental { double getCharge( int daysRented ) { double getCharge() { double result = 0; return _movie.getCharge( _daysRented ); switch (getPriceCode()) { } case Movie.REGULAR: result += 2; if (daysRented > 2) } result += (daysRented - 2) * 1.5; break; case Movie.NEW_RELEASE: result += daysRented * 3; break; case Movie.CHILDRENS: result += 1.5; if (daysRented > 3) result += (daysRented - 3) * 1.5; break; } return result; } } 55 56 28

Refactoring Refactoring class Rental { class Movie { int getFrequentRenterPoints() { int getFrequentRenterPoints( int daysRented ) { if ((getMovie().getPriceCode() == Movie.NEW_RELEASE) && if ((getPriceCode() == Movie.NEW_RELEASE) && getDaysRented() > 1) daysRented > 1) return 2; return 2; else else return 1; return 1; } } } } 57 58 29

Refactoring Refactoring class Rental { Get rid of the switch statement: int getFrequentRenterPoints() { return _movie.getFrequentRenterPoints( _daysRented ); } class Movie { } double getCharge( int daysRented ) { double result = 0; switch (getPriceCode()) { case Movie.REGULAR: result += 2; if (daysRented > 2) result += (daysRented - 2) * 1.5; break; case Movie.NEW_RELEASE: result += daysRented * 3; break; case Movie.CHILDRENS: result += 1.5; if (daysRented > 3) result += (daysRented - 3) * 1.5; break; } return result; } } 59 60 30

Refactoring Refactoring ? We have two flaws. What are they? Movie Hint: -priceCode : int +getCharge ( days: int ): double Is the movie classification static? Regular Movie Childrens Movie New Release Movie +getCharge ( days: int ): double +getCharge ( days: int ): double +getCharge ( days: int ): double 61 62 31

Refactoring Refactoring Flaw: Solution: A movie may change its classification Use State design pattern. during its lifetime. An object cannot change its class during its lifetime. 63 64 32

Refactoring Refactoring Movie * 1 Price Replace price (type) code: +getCharge( days: int ): double +getCharge( days: int ): double Apply Replace Type Code with State. Compile and test after each step. return price.getCharge ( days ) Regular Price Childrens Price New Release Price +getCharge( days: int ): double +getCharge( days: int ): double +getCharge( days: int ): double 65 66 33

Refactoring Refactoring public class Movie { Note: private int _priceCode; Make sure uses of the price type code go public Movie( String title, int priceCode ) { through accessor methods _title = title; _priceCode = priceCode; } public int getPriceCode() { return _priceCode; } public void setPriceCode( int arg ) { _priceCode = arg; } } 67 68 34

Refactoring Refactoring public class Movie { private int _priceCode; Add new state classes: abstract class Price { abstract int getPriceCode(); public Movie( String title, int priceCode ) { } _title = title; class RegularPrice extends Price { setPriceCode( priceCode ); int getPriceCode() { } public int getPriceCode() { return Movie.REGULAR; return _priceCode; } } } public void setPriceCode( int arg ) { class NewReleasePrice extends Price { _priceCode = arg; int getPriceCode() { } return Movie.NEW_RELEASE; } } } class ChildrensPrice extends Price { int getPriceCode() { return Movie.CHILDRENS; } } 69 70 35

Refactoring Refactoring public class Movie { Replace price type codes with instances private int _priceCode; of price state classes public int getPriceCode() { return _priceCode; } public void setPriceCode( int arg ) { _priceCode = arg; } } 71 72 36

Refactoring Refactoring public class Movie { private Price _price; Move getCharge() to Price class: public int getPriceCode() { Apply Move Method. return _price.getPriceCode(); } public void setPriceCode( int arg ) { switch (arg) { case REGULAR: _price = new RegularPrice(); break; case NEW_RELEASE: _price = new NewReleasePrice(); break; case CHILDRENS: _price = new ChildrensPrice(); break; default: throw new IllegalArgumentException( Incorrect price code ); } } } 73 74 37

Refactoring Refactoring class Movie { class Price { double getCharge( int daysRented ) { double getCharge( int daysRented ) { double result = 0; double result = 0; switch (getPriceCode()) { switch (getPriceCode()) { case Movie.REGULAR: case Movie.REGULAR: result += 2; result += 2; if (daysRented > 2) if (daysRented > 2) result += (daysRented - 2) * 1.5; result += (daysRented - 2) * 1.5; break; break; case Movie.NEW_RELEASE: case Movie.NEW_RELEASE: result += daysRented * 3; result += daysRented * 3; break; break; case Movie.CHILDRENS: case Movie.CHILDRENS: result += 1.5; result += 1.5; if (daysRented > 3) if (daysRented > 3) result += (daysRented - 3) * 1.5; result += (daysRented - 3) * 1.5; break; break; } } return result; return result; } } } } 75 76 38

Refactoring Refactoring class Movie { double getCharge( int daysRented ) { Replace switch statement in } return _price.getCharge( daysRented ); getCharge(): } For each case, add overriding method. Define abstract method. Apply Replace Conditional with Polymorphism. 77 78 39

Refactoring Refactoring class Price { class RegularPrice { double getCharge( int daysRented ) { double getCharge( int daysRented ) { double result = 2; double result = 0; switch (getPriceCode()) { if (daysRented > 2) case Movie.REGULAR: result += (daysRented - 2) * 1.5; result += 2; return result; if (daysRented > 2) } result += (daysRented - 2) * 1.5; } break; class NewReleasePrice { case Movie.NEW_RELEASE: result += daysRented * 3; double getCharge( int daysRented ) { break; return daysRented * 3; case Movie.CHILDRENS: } result += 1.5; } if (daysRented > 3) class ChildrensPrice { result += (daysRented - 3) * 1.5; double getCharge( int daysRented ) { break; double result = 1.5; } return result; if (daysRented > 3) } result += (daysRented - 3) * 1.5; } } } 79 80 40

Refactoring Refactoring class Price { Move getFrequentRenterPoints() to abstract double getCharge( int daysRented ); } Price class: Apply Move Method. 81 82 41

Refactoring Refactoring class Movie { class Price { int getFrequentRenterPoints( int daysRented ) { int getFrequentRenterPoints( int daysRented ) { if ((getPriceCode() == Movie.NEW_RELEASE) && if ((getPriceCode() == Movie.NEW_RELEASE) && daysRented > 1) daysRented > 1) return 2; return 2; else else return 1; return 1; } } } } 83 84 42

Refactoring Refactoring class Movie { int getFrequentRenterPoints( int daysRented ) { Replace if statement in } return _price.getFrequentRenterPoints( daysRented ); getFrequentRenterPoints(): } Apply Replace Conditional with Polymorphism. 85 86 43

Refactoring Refactoring class Price { class Price { int getFrequentRenterPoints( int daysRented ) { int getFrequentRenterPoints( int daysRented ) { if ((getPriceCode() == Movie.NEW_RELEASE) && return 1; daysRented > 1) } return 2; else } return 1; class NewReleasePrice { } int getFrequentRenterPoints( int daysRented ) { } return (daysRented > 1) ? 2 : 1; } } 87 88 44

Refactoring Refactoring Result of state design pattern: Benefits of second refactoring: easy to change price behavior easy to change movie classifications can add new price codes easy to change rules for charging and rest of application does not know about this frequent renter points use of the state pattern 89 90 45

-daysRented: int Rental * Customer Refactoring +getDaysRented(): int +statement() +getCharge(): double +htmlStatement() +getFrequentRenterPoints(): int +getTotalCharge(): double +getTotalFrequentRenterPoints(): int :Customer :Rental :Movie :Price * statement 1 Movie getTotalCharge() * 1 Price -price: Price * [for all rentals] getCharge getCharge ( days ) getCharge ( days ) +getCharge( days: int ): double +getCharge( days: int ): double +getFrequentRenterPoints( days: int ): int +getFrequentRenterPoints( days: int ): int getTotalFrequentRenterPoints * [for all rentals] getFrequentRenterPoints getFrequentRenterPoints ( days ) getFrequentRenterPoints ( days ) Regular Price Childrens Price New Release Price +getCharge( days: int ): double +getCharge( days: int ): double +getCharge( days: int ): double +getFrequentRenterPoints( days: int ): int 91 92 46

Bad Smells in Code Bad Smells in Code Data clumps: Feature envy: groups of data appearing together in the fields of a method seems more interested in a class classes, parameters to methods, etc. other than the one it is actually in e.g., int x, int y, int z e.g., invoking lots of get methods move these groups into their own class can use Extract Class and Introduce Parameter can use Move Method and Extract Method Object Example: group (start: Date, end: Date) into (aRange: RangeDate) 93 94 47

Bad Smells in Code Bad Smells in Code Primitive obsession: Switch statements: using the built-in types of the language too consider using polymorphism instead much e.g., conditionals on type codes defined in reluctance to use small objects for small other classes tasks e.g., zip code string can use Extract Method (on the switch), Move Method, Replace Type Code, and use objects for individual data values Replace Conditional with Polymorphism can use Replace Data Value with Object 95 96 48

Bad Smells in Code Bad Smells in Code Speculative generality: Message chains: I think we might need this someday. long chains of navigation to get to an e.g., abstract classes without a real purpose object e.g., unused parameters e.g., client object talks to server object that delegates to another object that the client object must also know about can use Collapse Hierarchy and Remove Parameter can use Hide Delegate 97 98 49

Bad Smells in Code Bad Smells in Code Middle man: Don t stand so close: a class that delegates many methods to two classes that depend too much on each another class other, with lots of bidirectional communication can use Remove Middle Man or Replace Delegation with Inheritance separate the two classes but could be a legitimate adapter can use Move Method, Move Field, and Extract Class (factor out commonality) 99 100 50

Bad Smells in Code Bad Smells in Code Alternative classes with different Data class: interfaces: classes that are all data (manipulated by other classes) methods that do the same thing but have e.g., a Point record that has other classes different signatures manipulating its coordinates e.g., put() versus add() in early stages, it s all right to use public fields can use Rename Method study usage and move behavior into data classes can use Encapsulate Field, Extract Method, Move Method 101 102 51

Bad Smells in Code Bad Smells in Code Refused bequest: Comments: when a subclass inherits something that is not often deodorant for bad smelling code needed when a superclass does not contain truly common state/behavior refactor code so that the comment becomes extraneous can use Push Down Method and Push Down Field can use Replace Inheritance with Delegation (e.g., Square versus Rectangle) 103 104 52

References Refactoring M. Fowler et al. Addison-Wesley, 1999 UML Distilled M. Fowler Addison-Wesley, 2000 105 53

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Refactoring Example

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