Adapter Design Pattern

Adapter Design Pattern

1. ADAPTER PATTERN Adeel Riaz (4632) Mirza Danish Baig (4577) Malik Mohammad Sohaib (4696) Farhan Ahmed (4719) Advisor: Muhammad Qasim pasta PAF KIET Fall 11 1

2. Real World Adapter Slide 2 PAF KIET Fall 11

3. Adapter in our Object Oriented Slide 3 PAF KIET Fall 11

4. Problem in Object Oriented?? Slide 4 PAF KIET Fall 11

5. Problem in Object Oriented?? Slide 5 I have already written class called xyzcircle that deals with circles already. But we can’t use directly because I want to preserve polymorphic behavior with Shape PAF KIET Fall 11

6. Problem in Object Oriented?? Slide 6 PAF KIET Fall 11 6

7. Intent Convert the interface of a class into another interface clients expect. Adapter lets classes work together that couldn't otherwise because of incompatible interfaces. Also Known As -> Wrapper Slide 7 PAF KIET Fall 11

8. Motivation Sometimes a toolkit or class library can not be used because its interface is incompatible with the interface required by an application We can not change the library interface, since we may not have its source code Even if we did have the source code, we probably should not change the library for each domain-specific application Slide 8 PAF KIET Fall 11

9. Motivation Example: Slide 9 PAF KIET Fall 11

10. Applicability Use the Adapter pattern when You want to use an existing class, and its interface does not match the one you need You want to create a reusable class that cooperates with unrelated classes with incompatible interfaces Slide 10 PAF KIET Fall 11

11. Structure An object adapter relies on object composition: Slide 11 PAF KIET Fall 11

12. Participants Target (Shape) defines the domain-specific interface that Client uses. Adapter (Line,TextShape) adapts the interface Adaptee to the Target interface. Adaptee (TextView) defines an existing interface that needs adapting. Client (DrawingEditor) collaborates with objects conforming to the Target interface. Slide 12 PAF KIET Fall 11

13. Example Slide 13 PAF KIET Fall 11

14. Example Slide 14 PAF KIET Fall 11

15. Sequence Diagram Slide 15 PAF KIET Fall 11

16. Consequences Class adapter Concrete Adapter class Unknown Adaptee subclasses might cause problem Object adapter Adapter can service many different Adaptees May require the creation of Adaptee subclasses and referencing those objects Slide 16 PAF KIET Fall 11

17. Implementation slide 17 How much adapting should be done? Simple interface conversion that just changes operation names and order of arguments Totally different set of operations Does the adapter provide two-way transparency? A two-way adapter supports both the Target and the Adaptee interface. It allows an adapted object (Adapter) to appear as an Adaptee object or a Target object PAF KIET Fall 11

18. Comparing the Facade Pattern with the Adapter Pattern Slide 18 In both the Facade and Adapter pattern I have preexisting classes. In the Facade, however, I do not have an interface I must design to, as I do in the Adapter pattern. I am not interested in polymorphic behavior in the Façade, while in the Adapter, I probably am. (There are times when we just need to design to a particular API and therefore must use an Adapter. In this case, polymorphism may not be an issue— that's why I say "probably"). In the case of the Facade pattern, the motivation is to simplify the interface. With the Adapter, while simpler is better, I am trying to design to an existing interface and cannot simplify things even if a simpler interface were otherwise possible. PAF KIET Fall 11

19. Example 1 slide 19 Consider that we have a third party library that provides sorting functionality through it's NumberSorter class. This is our Adaptee /* * This is our adaptee , a third party implementation of a * number sorter that deals with Lists, not arrays . */ public class NumberSorter { public List<Integer> sort(List<Integer> numbers ) { // sort and return return new ArrayList <Integer >(); } } PAF KIET Fall 11

20. Example 1 (continued) slide 20 Our Client deals with primitive arrays rather than Lists. For the sake of this example, lets say we can't change the client to use Lists . We've provided a Sorter interface that expects the client input. This is our target. // this is our Target interface public interface Sorter { public int [] sort( int [] numbers ); } PAF KIET Fall 11

21. Example 1 (continued) slide 21 Finally, the SortListAdapter implements our target interface and deals with our adaptee , NumberSorter public class SortListAdapter implements Sorter { @Override public int [] sort( int [] numbers ) { // convert the array to a List List<Integer > numberList = new ArrayList <Integer >(); // call the adapter NumberSorter sorter = new NumberSorter (); numberList = sorter.sort ( numberList ); // convert the list back to an array and return return sortedNumbers ; } } PAF KIET Fall 11

22. Example 1 (Continued) slide 22 int [] numbers = new int []{34, 2, 4, 12, 1}; Sorter sorter = new SortListAdapter (); sorter.sort (numbers ); PAF KIET Fall 11

23. Questions? slide 23 PAF KIET Fall 11