Adapter Pattern Tutorial

What is the Adapter Design Pattern?

The Adapter Design Pattern is a structural design pattern employed to enable collaboration between two otherwise incompatible interfaces. It is frequently utilized when an existing system or class needs to be reused, but its interface does not align with the rest of the system. Instead of altering the existing system, which may not be feasible or desirable, an adapter can be created to serve as a bridge between the existing component and the new system.

The adapter comprises two primary elements: an interface that matches the system it is adapting to, and an implementation that translates calls from the adapted system to the existing system. This translation facilitates seamless communication and cooperation between the two systems.

The Adapter Design Pattern can be implemented using two main approaches: class adapters and object adapters. Class adapters leverage multiple inheritance to adapt one interface to another, whereas object adapters achieve the same outcome through composition. Both methods have their respective advantages and disadvantages, and the choice between them depends on the specific requirements of the system.

Overall, the Adapter Design Pattern is an invaluable tool for integrating existing systems and classes into new software systems without requiring modifications to the original components. It is a powerful technique that promotes code reuse and helps in building more robust software architectures.

Modeling the Design Pattern with a Class Diagram

1. Create a new project named Design Patterns.
2. Create a class diagram named Adapter.
   
3. Select Class from the diagram toolbar. Click on the diagram to create a class and name it Client.
   
4. Move the mouse cursor over the Client class, and drag out Association > Class to create an associated class named Target.
   
5. Right-click on Target, and select Model Element Properties > Abstract to set it as abstract.
   
6. Right-click on the Target class, and select Add > Operation from the popup menu.
   
7. Name the operation Request().
8. Right-click on Request, and select Model Element Properties > Abstract to set it as abstract.
   
9. Move the mouse cursor over the Target class, and drag out Generalization > Class to create a subclass named Adapter.
   
10. The Adapter will inherit operations from Target. Right-click on Adapter and select Related Elements > Realize all Interfaces from the popup menu.
    
11. Move the mouse cursor over the Adapter class, and drag out Association > Class to create an associated class named Adaptee.
    
12. In practice, there may be multiple requests. To represent this, stereotype the class Target as PTN Members Creatable. Right-click on Target and select Stereotypes > Stereotypes... from the popup menu.
    
13. In the Stereotype tab of the Class Specification dialog box, select PTN Members Creatable and click the right arrow to assign it to the Target class. Click OK to confirm.
    
    At this point, the diagram should look like this:
    

Defining the 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 Adapter. Keep the file name as is. Click OK to proceed.
   

Applying the Design Pattern to a Class Diagram

In this section, we will apply the Adapter pattern to wrap a legacy Shape class.

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.
   
4. In the Design Pattern dialog box, select Adapter from the list of patterns.
   
5. Click on Target in the overview pane.
   
6. Rename Target to Shape, and its operation Request to getColor in the bottom pane.
   
7. Besides the operation getColor, we also require two more operations: getPosition and draw. With Target still selected, click the + button at the bottom pane, and select New Operation... from the popup menu.
   
8. In the Operation Specification dialog box, name the operation getPosition. Check the Abstract option at the bottom of the dialog box.
   
9. Repeat steps 7 and 8 to create the operation draw.
   
10. Select Adapter in the overview, and rename it as NewShape in the bottom pane. Also rename the operation Request to getColor. Note that if the Auto Rename option is enabled, renaming the operation is not necessary as it will be handled automatically.
    
11. Select Adaptee in the overview, and rename it as LegacyShape in the bottom pane. Click OK to apply the pattern to the diagram.
    
12. We need to create specific requests within LegacyShape. Select the operations in NewShape.
    
13. Press and hold the Ctrl key, then drag the selected operations to LegacyShape to copy them.
    This is the result: