Factory Method Pattern Tutorial

Modeling a Design Pattern with a Class Diagram

1. Create a new project named Design Patterns.
2. Create a class diagram named Factory Method.
   
3. Select Class from the diagram toolbar. Click on the diagram to create a class. Name it Product.
   
4. Set the Product class as abstract by right-clicking on it and selecting Model Element Properties > Abstract from the popup menu.
   
5. Move the mouse cursor over the Product class and drag out Generalization > Class to create a subclass named ConcreteProduct.
   
6. Create a class named Creator and set it as abstract.
   
7. Right-click on the Creator class and select Add > Operation from the popup menu.
   
8. Name the operation FactoryMethod() and make it return Product.
9. Right-click on FactoryMethod() and select Model Element Properties > Abstract to set it as abstract.
   
10. Add a non-abstract operation AnOperation() to Creator.
    
11. Move the mouse cursor over the Creator class and drag out Generalization > Class to create a subclass named ConcreteCreator.
12. Make ConcreteCreator inherit the abstract operations provided by Creator by right-clicking on ConcreteCreator and selecting Related Elements > Realize all Interfaces from the popup menu.
    
13. In practice, the FactoryMethod in ConcreteCreator is expected to return an instance of ConcreteProduct. Therefore, add a dependency between ConcreteCreator and ConcreteProduct. Move the mouse cursor over the ConcreteCreator class and drag out Dependency > Class to ConcreteProduct. Up to now, the diagram should look like this:
    
14. There may be more than one operation in the Creator class. To represent this, stereotype the Creator class as PTN Members Creatable. Right-click on the Creator class and select Stereotypes > Stereotype from the popup menu.
    
15. In the Stereotypes tab of the class specification, select PTN Members Creatable and click > to assign it to the class. Click OK to confirm.
    
16. The Product class should also have its own operations. Repeat steps 14 and 15 to stereotype it as PTN Members Creatable.
17. There may be multiple concrete products and creators. Let's repeat steps 14 and 15 to stereotype ConcreteProduct and ConcreteCreator as PTN Cloneable. The diagram should look like this:
    

Defining a Pattern

1. Select all classes on the class diagram.
   
2. Right-click on the selection and select Define Design Pattern... from the popup menu.
   
3. In the Define Design Pattern dialog box, specify the pattern name as Factory Method. Keep the file name as is. Click OK to proceed.
   

Applying a Design Pattern to a Class Diagram

In this section, we will try to use the factory method pattern to model a part of a text editor.

1. Create a new project named Text Editor.
2. Create a class diagram named Domain Model.
3. Right-click on the class diagram and select Utilities > Apply Design Pattern... from the popup menu.
   
4. In the Design Pattern dialog box, select Factory Method from the list of patterns.
   
5. Click on Product in the overview.
   
6. Rename it to TextDocument in the bottom pane.
   
7. Click on +, and select New Operation... from the popup menu. We will create the operations available in the TextDocument class.
   
8. In the Operation Specification dialog box, enter Open as the operation name.
   
9. Repeat steps 7 and 8 to create operations close, save, and reopen.
   
10. Click on ConcreteProduct in the overview.
11. Rename ConcreteProduct to PlainTextDocument.
    
12. We need to process one more document type for RTF documents. Keep ConcreteProduct selected and click the + button, then select Clone... from the popup menu.
    
13. Enter 1 as the number of classes to clone. Click OK to confirm.
    
14. Enter RTFDocument as the class name.
    
15. Select the Creator class in the overview.
16. Rename Creator to TextEditor, the operation FactoryMethod to createDoc, and AnOperation to newDoc.
    
17. We need more operations. Click on +, then select New Operation... from the popup menu.
    
18. In the Operation Specification dialog box, enter loadDoc as the name.
    
19. Repeat the previous steps to create operations closeDoc, saveDoc, and reopenDoc.
    
20. Select ConcreteCreator. Rename ConcreteCreator to MyTextEditor and the operation FactoryMethod to createDoc.
    
21. Click OK to confirm editing and apply the pattern to the diagram.
22. Tidy up the diagram. It should look like this: