Factory Method Pattern

1. Factory Method Pattern Mohammed Al-Dhelaan CSci 253 Object Oriented Design Instructor: Brad Taylor 06/02/2009

2. Overview • Introduction • Factory Method • Structure • Implementation • Example • Conclusion • References

3. Introduction • Reusability is a goal for design patterns • Design patterns help programmers identify reoccurring design issues • Design Patterns also help insure encapsulation and information hiding • Factory method pattern is an object oriented design pattern. • It’s considered a creational pattern

4. Factory Method • The problem: • We don’t know when to instantiate object! • Factory method defers instantiation to subclasses • It’s goal is when to instantiate more than what to instantiate • Uses an interface that decides what subclass to choose, then instantiate an object from the subclass that was chosen

5. Factory Method • The user code doesn’t create objects • The factory method instantiates objects • Determination of what class to instantiate is handled at runtime

6. Factory Method • When to use the Factory Method pattern: • The superclass cannot determine what class to instantiate objects from • The superclass wants its subclass to specify the objects • Factory Method pattern helps hiding the core classes from clients

7. Structure

8. Implementation • The Creator class is designed as an abstract class • No implementation for the abstract class • Subclasses must have an implementation that deals with the Factory Method

9. Implementation

10. Implementation • publicabstractclass Profile { • public Profile (String sName, String sEmail){ • m_sName = sName; • m_sEmail = sEmail; • } • public String getName() {returnm_sName;} • public String getEmail() {returnm_sEmail;} • publicbooleanIsEmployee() {returnm_bIsEmployee;} • publicabstract Resource getResource(); • protected String m_sName, • m_sEmail; • protectedbooleanm_bIsEmployee; • } • Reference  Goplan Suresh Raj

11. Implementation • The Creator class is designed as a concrete class • Create the object then let the subclass overrides it • More flexible • Involves the concept of overriding

12. Implementation • Using a parameterized Factory Method • In this implementation we have to use an identifier • From that identifier we can know what object to create

13. Implementation • public class ResourceCreator { • public static final int CONFIDENTIAL = 0; • public static final int PUBLIC = 1; • public Resource createResource (intnID) { • switch (nID) { • case CONFIDENTIAL: • return new ConfidentialResource (); • case PUBLIC: • return new PublicResource (); • } • return null; • } • } • Reference  Goplan Suresh Raj

14. Implementation • public class Employee extends Profile { • public Employee (String sName, String sEmail) { • super (sName, sEmail); • m_bIsEmployee = true; • } • public Resource getResource () { • ResourceCreator creator = new ResourceCreator (); • return creator.createResource (ResourceCreator.CONFIDENTIAL); • } • } • Reference  Goplan Suresh Raj

15. Implementation • public class NonEmployee extends Profile { • public NonEmployee (String sName, String sEmail) { • super (sName, sEmail); • m_bIsEmployee = false; • } • public Resource getResource () { • ResourceCreator creator = new ResourceCreator (); • return creator.createResource (ResourceCreator.PUBLIC); • } • } • Reference  Goplan Suresh Raj

16. Implementation • Templates instead of subclasses • C++ • Naming conventions • Good for readability

17. Example

18. Example • public class Person { • // name string • public String name; • // gender : M or F • private String gender; • public String getName() { • return name; • } • public String getGender() { • return gender; • } • }// End of class

19. Example • public class Male extends Person { • public Male(String fullName) { • System.out.println("Hello Mr. "+fullName); • } • }// End of class • public class Female extends Person { • public Female(String fullNname) { • System.out.println("Hello Ms. "+fullNname); • } • }// End of class

20. Example • public class SalutationFactory { • public static void main(String args[]) { • SalutationFactory factory = new SalutationFactory(); • factory.getPerson(args[0], args[1]); • } • public Person getPerson(String name, String gender) { • if (gender.equals("M")) • return new Male(name); • else if(gender.equals("F")) • return new Female(name); • else • return null; • } • }// End of class

21. Conclusion • Introduction • Factory Method • Structure • Implementation • Example • Conclusion • References

22. References • Gamma, Erich; Helm, Richard; Johnson, Ralph; Vlissides, John (1994). Design Patterns: Elements of Reusable Object-Oriented Software. Addison-Wesley. ISBN 0-201-63361-2.  • Raj, Goplan Suresh. http://gsraj.tripod.com/design/creational/factory/factory.html • AllAppLaps.com. http://www.allapplabs.com/java_design_patterns/factory_pattern.htm • Tarr, Bob. Factory Patterns. http://userpages.umbc.edu/~tarr/dp/lectures/Factory.pdf