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Desing pattern prototype-Factory Method, Prototype and Builder

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Desing pattern prototype-Factory Method, Prototype and Builder

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Desing pattern prototype-Factory Method, Prototype and Builder

  1. 1. Design Pattern Introduction Factory Method, Prototype & Builder Design Pattern -ParamiSoft Systems Pvt. Ltd.
  2. 2. Agenda • Factory Method Pattern o Introduction o When to consider? o Example o Limitations Prototype Pattern o Introduction o Applicability o Consequences o Example Prototype Pattern o Introduction o Example o Discussion -ParamiSoft Systems Pvt. Ltd.
  3. 3. The Gang of Four: Pattern Catalog Creational Abstract Factory Builder Factory Method Prototype Singleton Structural Adapter Bridge Composite Decorator Façade Flyweight Proxy Behavioral Chain of Responsibility Command Interpreter Iterator Mediator Memento Observer State Strategy Template Method Visitor Patterns in red we will discuss in this presentation -ParamiSoft Systems Pvt. Ltd.
  4. 4. Factory Method -ParamiSoft Systems Pvt. Ltd.
  5. 5. -ParamiSoft Systems Pvt. Ltd. • Name: Factory Method • Intent: Define an interface for creating an object, but let subclasses decide which class to instantiate. Defer instantiation to subclasses. • Problem: A class needs to instantiate a derivation of another class, but doesn't know which one. Factory Method allows a derived class to make this decision. • Solution: Provides an abstraction or an interface and lets subclass or implementing classes decide which class or method should be instantiated or called, based on the conditions or parameters given. Factory Method
  6. 6. -ParamiSoft Systems Pvt. Ltd. When to consider? • When we have a class that implements an interface but not sure which object, which concrete instantiation / implementation need to return. • When we need to separate instantiation from the representation. • When we have lots of select and switch statements for deciding which concrete class to create and return.
  7. 7. -ParamiSoft Systems Pvt. Ltd. Factory Says Define an interface for creating an object, but let subclasses decide which class to instantiate
  8. 8. -ParamiSoft Systems Pvt. Ltd. public interface ConnectionFactory{ public Connection createConnection(); } class MyConnectionFactory implements ConnectionFactory{ public String type; public MyConnectionFactory(String t){ type = t; } public Connection createConnection(){ if(type.equals("Oracle")){ return new OracleConnection(); } else if(type.equals("SQL")){ return new SQLConnection(); } else{ return new MySQLConnection(); } } } Implementation: ConnectionFactory
  9. 9. -ParamiSoft Systems Pvt. Ltd. public interface Connection{ public String description(); public void open(); public void close(); } class SQLConnection implements Connection{ public String description(){ return "SQL";} } class MySQLConnection implements Connection{ public String description(){ return "MySQL” ;} } class OracleConnection implements Connection{ public String description(){ return "Oracle"; } } Implementation: ConnectionFactory
  10. 10. -ParamiSoft Systems Pvt. Ltd. class TestConnectionFactory{ public static void main(String[]args){ MyConnectionFactory con = new MyConnectionFactory("My SQL"); Connection con2 = con.createConnection(); System.out.println("Connection Created: "); System.out.println(con2.description()); } } Implementation: ConnectionFactory
  11. 11. -ParamiSoft Systems Pvt. Ltd. • Refactoring an existing class to use factories breaks existing clients. • Since the pattern relies on using a private constructor, the class cannot be extended • if the class were to be extended (e.g., by making the constructor protected—this is risky but feasible), the subclass must provide its own re-implementation of all factory methods with exactly the same signatures. Limitations
  12. 12. Prototype Design Pattern -ParamiSoft Systems Pvt. Ltd.
  13. 13. Prototype Design Pattern Specify the kinds of objects to create using a prototypical instance, and create new objects by copying this prototype -ParamiSoft Systems Pvt. Ltd.
  14. 14. Structure -ParamiSoft Systems Pvt. Ltd.
  15. 15. Applicability -ParamiSoft Systems Pvt. Ltd. • Avoid subclasses of an object creator in the client application • Avoid the inherent cost of creating new object in the standard way eg. Using new keyword • Alternative to Factory Method and Abstract Factory. • Can be used to implement Abstract Factory. • To avoid building a class hierarchy of factories. • Can be used when loading classes dynamically • Often can use class objects instead.
  16. 16. Consequences -ParamiSoft Systems Pvt. Ltd. • Add/Remove prototypes at runtime. • Specify new prototypes by varying data. • Specify new prototypes by varying structure. • Less classes (less sub-classing!) • Dynamic class loading.
  17. 17. Psudocode -ParamiSoft Systems Pvt. Ltd. class WordOccurrences is field occurrences is The list of the index of each occurrence of the word in the text. constructor WordOccurrences(text, word) is input: the text in which the occurrences have to be found input: the word that should appear in the text Empty the occurrences list for each textIndex in text isMatching := true for each wordIndex in word if the current word character does not match the current text character then isMatching := false if isMatching is true then Add the current textIndex into the occurrences list
  18. 18. Psudocode -ParamiSoft Systems Pvt. Ltd. method getOneOccurrenceIndex(n) is input: a number to point on the nth occurrence. output: the index of the nth occurrence. Return the nth item of the occurrences field if any. method clone() is output: a WordOccurrences object containing the same data. Call clone() on the super class. On the returned object, set the occurrences field with the value of the local occurrences field. Return the cloned object. text := "The prototype pattern is a creational design pattern in software development first described in design patterns, the book." word := "pattern" searchEngine := new WordOccurrences(text, word) anotherSearchEngine := searchEngine.clone()
  19. 19. Builder Design Pattern -ParamiSoft Systems Pvt. Ltd.
  20. 20. -ParamiSoft Systems Pvt. Ltd. • Name: Builder • Intent: The intent of the Builder design pattern is to separate the construction of a complex object from its representation. By doing so, the same construction process can create different representations Builder
  21. 21. -ParamiSoft Systems Pvt. Ltd. The builder pattern is an object creation design pattern. Unlike the abstract factory and factory method pattern whose intention is to enable polymorphism, the intention of the builder pattern is to find a solution to the telescoping constructor anti- pattern. The telescoping constructor anti-pattern occurs when the increase of object constructor parameter combinations leads to an exponential list of constructors. Instead of using numerous constructors, the builder pattern user another object. A builder that receives each initialization parameter step by step and then returns the resulting constructed object at once Description
  22. 22. Psudocode -ParamiSoft Systems Pvt. Ltd. class Car is Can have GPS, trip computer and various numbers of seats. Can be a city car, a sports car, or a cabriolet. class CarBuilder is method getResult() is output: a Car with the right options Construct and return the car. method setSeats(number) is input: the number of seats the car may have. Tell the builder the number of seats. method setCityCar() is Make the builder remember that the car is a city car. method setCabriolet() is Make the builder remember that the car is a cabriolet. method setSportsCar() is Make the builder remember that the car is a sports car.
  23. 23. Psudocode -ParamiSoft Systems Pvt. Ltd. method setTripComputer() is Make the builder remember that the car has a trip computer. method unsetTripComputer() is Make the builder remember that the car does not have a trip computer. method setGPS() is Make the builder remember that the car has a global positioning system. method unsetGPS() is Make the builder remember that the car does not have a global positioning system. Construct a CarBuilder called carBuilder carBuilder.setSeats(2) carBuilder.setSportsCar() carBuilder.setTripComputer() carBuilder.unsetGPS() car := carBuilder.getResult()
  24. 24. Discussion -ParamiSoft Systems Pvt. Ltd. • Factory Method: delegate to subclasses. • AbstractFactory, Builder, and Prototype: delegate to another class. • Prototype: reduces the total number of classes. • Builder: Good when construction logic is complex.
  25. 25. References Links o http://en.wikipedia.org/wiki/Factory_method_pattern o http://en.wikipedia.org/wiki/Prototype_pattern o http://en.wikipedia.org/wiki/Builder_pattern o http://sourcemaking.com/design_patterns Links o Design Patterns in Ruby – Russ Olsen o Head First Design Patterns – Elisabeth Freeman, Eric Freeman, Bert Bates and Kathy Sierra -ParamiSoft Systems Pvt. Ltd.
  26. 26. If(Questions) { Ask; } else { Thank you; } -ParamiSoft Systems Pvt. Ltd.

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