Chapter Seven The Adapter Pattern

1. Chapter SevenThe Adapter Pattern Ku-Yaw Chang canseco@mail.dyu.edu.tw Assistant Professor, Department of Computer Science and Information Engineering Da-Yeh University

2. Outline • Introducing the Adapter Pattern • Learning the Adapter Pattern • Field Notes: The Adapter Pattern • Summary The Adapter Pattern

3. Introducing the Adapter Pattern • Intent by GoF • Convert the interface of a class into another interface that the clients expect. Adapter lets classes work together that could not otherwise because of incompatible interfaces. • Also known as Wrapper The Adapter Pattern

4. Outline • Introducing the Adapter Pattern • Learning the Adapter Pattern • Field Notes: The Adapter Pattern • Summary The Adapter Pattern

5. Learning the Adapter Pattern • Consider the following requirements • Create classes for points, lines, and squares that have the behavior “display.” • The client objects should not have to know whether they actually have a point, a line, or a square. They just want to know that they have one of these shapes. The Adapter Pattern

6. Learning the Adapter Pattern • Encompass these specific shapes in a higher-level concept that I will call a “displayable shape.” The Adapter Pattern

7. The Adapter Pattern • Make use of polymorphism • Specify the particular behavior that Shapes are going to provide. • Set a Shape’s location. • Get a Shape’s location. • Display a Shape. • Fill a Shape. • Set the color of a Shape. • Undisplay a Shape. The Adapter Pattern

8. The Adapter Pattern The Adapter Pattern

9. The Adapter Pattern • XXCircle with the following methods • displayIt • fillIt • undisplayIt • Cannot use XXCircle directly • I have different names and parameter lists • I cannot derive it • What can I do? • I have what I want almost within reach, but I cannot use it and I do not want to rewrite it. The Adapter Pattern

10. The Adapter Pattern • Rather than change it, I adapt it. • Class Circle derives from Shape • Circle contains XXCircle • Circle passes requests made to the Circle object on through to the XXCircle object. The Adapter Pattern

11. Implementation The Adapter Pattern

12. Outline • Introducing the Adapter Pattern • Learning the Adapter Pattern • Field Notes: The Adapter Pattern • Summary The Adapter Pattern

13. Field Notes: The Adapter Pattern • You can do more than wrapping. • Functions in the existing class can be adapted • Functions not present can be implemented in the wrapping object • Free you from worrying about existing interfaces • Variations • Object adapter pattern • Rely on one object containing another • Class adapter pattern • Multiple inheritance The Adapter Pattern

14. Comparing the Adapterwith the Facade • Both are wrappers • Subtle differences The Adapter Pattern

15. Outline • Introducing the Adapter Pattern • Learning the Adapter Pattern • Field Notes: The Adapter Pattern • Summary The Adapter Pattern

16. The Adapter Pattern • A Facade simplifies an interface while an Adapter converts the interface into a preexisting interface. • A very useful pattern that converts the interface of a class (or classes) into another interface, which we need the class to have. • Be implemented by creating a new class with the desired interface and then wrapping the original class methods to effectively contain the adapted object. The Adapter Pattern

17. The End