Factory Method Pattern

1. CSci 658Software Language EngineeringFactor Method Design PatternSpring Semester 2018Lecture Notes

2. Factory Method Pattern This is a set of slides to accompany chapter 8 of Mark Grand’s book Patterns in Java : a catalog of reusable design patterns illustrated with UML (John Wiley & Sons, 1998) Created: 19 August 2004 Revised: 20 April 2010, 8 February 2018

3. Context • A reusable application that must work with objects from different subclasses of a base class • Wish to keep application independent of the actual subclass being used • Invoke only operations on the base class • Delegate creation of the actual subclass object to a special class – factory 1

4. Application uses uses creates NameFactory Namer FirstFirst LastFirst A Simple Factory 2

5. A Simple Factory (cont.) public class Namer { public String getFirst () { return first; } public String getLast () { return last; } protected void setFirst ( String f) { first = f; } protected void setLast (String l) { last = l; } private String first; private String last; } 3

6. A Simple Factory (cont.) public class FirstFirst extends Namer { public FirstFirst (String s) { int i = s.lastIndexOf (" "); if (i > 0) { setFirst (s.substring(0, i).trim() ); setLast (s.substring(i+1).trim() ); } else { setFirst (" "); setLast(s); } } } 4

7. A Simple Factory (cont.) public class LastFirst extends Namer { public LastFirst (String s) { int i = s. indexOf (","); if (i > 0) { setFirst (s.substring(i+1).trim() ); setLast (s.substring(0,i).trim() ); } else { setFirst (" "); setLast(s); } } } 5

8. A Simple Factory (cont.) public class NameFactory { public Namer gerNamer (String s) { int i = s. indexOf (","); if (i > 0) return new LastFirst(s); else return new FirstFirst(s); } } 6

9. A Simple Factory (cont.) • Application … NameFactory nf = new NameFactory (); … Namer n = nf.getNamer(s); … String l = n.getLast(); 7

10. Application independent class Product operation1 opertation2 … CreationRequestor newDocument … Uses * 1 abstract superclass requestor 1 Requests_creation Application independent interface * Concrete class instantiated by objects creator * <<interface>>FactoryIF createProduct (discriminator):Product ConcreteProduct operation1 opertation2 … Application-specific class. Implement factory interface. Has method to create ConcreateProduct objects Factory createProduct (discriminator):Product 1 Creates Solution 8

11. Consequences • Creation-requestor class independent from concrete product class • Set of product classes may change • only affects factory class 9

12. Acknowledgement • Acxiom Corporation supported the creation of this presentation as part of a grant titled “The Acxiom Laboratory for Software Architecture and Component Engineering (ALSACE).” • The research team consisted of Dr. Conrad Cunningham, PhD students Yi Liu and PallaviTadepalli, and MS students Mingxian Fu and Hui Xiong. 10