Bridge Pattern Tutorial

This tutorial is aimed to guide the definition and application of Gang of Four (GoF) bridge design pattern. By reading this tutorial, you will know how to develop a model for the bridge pattern, and how to apply it in practice.

October 8, 2009
Views: 49,101
PDF Download
Compatible: Enterprise, Professional, Standard

Modeling a Design Pattern with a Class Diagram

  1. Create a new project called Design Patterns.
  2. Create a class diagram named Bridge.
    new diagram
  3. Select Class from the diagram toolbar. Click on the diagram to create a class. Name it Abstraction.
    create abstraction class
  4. Right-click on Abstraction and select Model Element Properties > Abstract to set it as abstract.
    set abstraction abstract
  5. Move the mouse cursor over the Abstraction class and drag out Aggregation > Class to create an associated class named Implementor.
    create implementor
  6. Right-click on Implementor and select Model Element Properties > Abstract to set it as abstract.
  7. Right-click on the Abstraction class and select Add > Operation from the popup menu.
    add oper to abstraction
  8. Name the operation Operation().
  9. Right-click on the Implementor class and select Add > Operation from the popup menu. Name the operation OperationImpl().
    create operation impl
  10. Right-click on Implementor and select Model Element Properties > Abstract to set it as abstract.
    set operation impl abstract
  11. Move the mouse cursor over the Abstraction class and drag out Generalization > Class to create a subclass named RefinedAbstraction.
    create refined abstraction
  12. Repeat the previous step to create a subclass named ConcreteImplementor from Implementor.
    create concrete implementor
  13. ConcreteImplementor will inherit the operations from Implementor. Right-click on ConcreteImplementor and select Related Elements > Realize all Interfaces from the popup menu.
    realize implementor
  14. In practice, there may be multiple refined abstractions and/or concrete implementors. To represent this, stereotype the RefinedAbstraction and ConcreteImplementor classes as PTN Cloneable. Right-click on Abstraction and select Stereotypes > Stereotypes... from the popup menu.
    set abstract stereotype
  15. In the Stereotypes tab of the Class Specification dialog box, select PTN Cloneable and click > to assign it to the RefinedAbstraction class. Click OK to confirm.
    set PTN cloneable
  16. Repeat steps 14 and 15 for ConcreteImplementor.
    pattern modeled
  17. In practice, there may be multiple operations and/or operationImpls. To represent this, stereotype the Abstraction and Implementor classes as PTN Members Creatable. Repeat steps 14 and 15 to stereotype Abstraction and Implementor as PTN Members Creatable.

Defining a Pattern

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

Applying a Design Pattern to a Class Diagram

In this section, we will apply the bridge pattern to model a report generator for various report types.

  1. Create a new project named Diagram 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.
    apply design pattern
  4. In the Design Pattern dialog box, select Bridge from the list of patterns.
    select bridge
  5. Click on Abstraction in the overview.
    select abstraction
  6. Rename Abstraction to ReportGenerator and the Operation operation to generate in the bottom pane.
    rename abstraction
  7. Select RefinedAbstraction in the overview pane.
  8. Rename RefinedAbstraction to HTMLReportGenerator.
    rename generator
  9. In addition to the HTML report generator, we also need a Plain Text report generator. Click the + button in the bottom pane, next to Abstraction, and select Clone...
    select clone
  10. Enter 1 as the number of classes to clone and click OK to confirm.
    enter no of classes to clone
  11. Rename the cloned class, RefinedAbstraction2, to PlainTextReportGenerator.
    plain text rpt generator
  12. Select Implementor in the overview pane.
  13. Rename Implementor to ReportGeneratorImpl and OperationImpl to generateTOC.
    rename implementor
  14. We need two more operations for generating the content and appendix. Click the + button and select New Operation... from the popup menu.
    new oper
  15. In the Operation Specification dialog box, name the operation generateContent. Check the Abstract box at the bottom of the dialog.
    new gen content
  16. Repeat the previous steps to create another abstract operation named generateAppendix.
    opers defined in implementor
  17. Select ConcreteImplementor in the overview. Rename ConcreteImplementor to SimpleReportGeneratorImpl and the OperationImpl operation to generateTOC.
    rename concrete implementor
  18. Similar to RefinedAbstraction, we need another concrete implementor for generating complex reports. Click the + button and select Clone... from the popup menu.
    select clone
  19. Enter 1 as the number of classes to clone and click OK to confirm.
  20. Rename the cloned class, ConcreteImplementor2, to ComplexReportGeneratorImpl, and the OperationImpl operation to generateTOC.
    complex report generator created
  21. Click OK to confirm. The diagram should now look like this:
    diagram formed
  22. We want HTMLReportGenerator and PlainTextReportGenerator to implement their own way of generating reports. Select the "generate" operation in ReportGenerator.
    select generate in report generator
  23. Press the Ctrl key and drag it to HTMLReportGenerator. Release the mouse button afterward.
    duplicate generate
  24. Repeat the previous steps to create the "generate" method in PlainTextReportGenerator. The completed diagram should look like this:
    complete diagram
Resources
  1. Bridge.pat
  2. Design Patterns.vpp
Related Links