- Create a new project Design Patterns.
- Create a class diagram Chain of Responsibility.
- Select Class from diagram toolbar. Click on the diagram to create a class. Name it as Client.
- Move the mouse cursor over the Client class, and drag out Association > Class to create an associated class Handler.
- Right click on Handler, and select Model Element Properties > Abstract to set it as abstract.
- Right click on Handler class, and select Add > Operation from the popup menu.
- Name the operation HandleRequest().
- Right click on HandleRequest, and select Model Element Properties > Abstract to set it as abstract.
- Move the mouse cursor over the Handler class, and click on the resource icon Self Association to create a self association.
- Name the association end successor.
- Move the mouse cursor over the Handler class, and drag out Generalization > Class to create subclasses ConcreteHandler.
- In practice, there may be multiple concrete handlers. To represent this, stereotype the class ConcreteHandler as PTN Cloneable. Right click on ConcreteHandler and select Stereotypes > Stereotype... from the popup menu.
- In the Stereotypes tab of the Class Specification dialog box, select PTN Cloneable and click > to assign it to ConcreteHandler class. Click OK to confirm.
We need make the concrete handlers inherit operations from the handle class. Right click on ConcreteHandler and select Related Elements > Realize all Interfaces from the popup menu.
Up to now, the diagram should look like this:
- Select all classes on the class diagram.
- Right click on the selection and select Define Design Pattern... from the popup menu.
- In the Define Design Pattern dialog box, specify the pattern name Chain of Responsibility. Keep the file name as is. Click OK to proceed.
In this section, we are going to apply the chain of responsibility pattern in modeling a coin dispenser.
- Create a new project Coin Dispenser.
- Create a class diagram Domain Model.
- Right click on the class diagram and select Utilities > Apply Design Pattern... from the popup menu.
- In the Design Pattern dialog box, select Chain of Responsibility from the list of patterns.
- Click on Handler in the overview.
- Rename Handler to CoinDispenser, and operation HandleRequest to Dispense at the bottom pane.
- Click on ConcreteHandler in overview, and rename it to DollarDispenser, and operation HandleRequest to Dispense.
- We need one more concrete handler for dispensing cents. Keep ConcreteHandler selected, click on + and select Clone... from the popup menu.
- Enter 1 to be the number of classes to clone. Click OK to confirm.
- Rename ConcreteHandler2 to CentDispenser, and operation HandleRequest to Dispense.
- Click OK to apply the pattern to diagram.
- Tidy up the diagram. Here is the result: