1. Software Design
Lecture : 34

2. Structural Design Patterns
They deal with how classes and objects deal with to form large structures.
Structural Design patterns use inheritance to compose interfaces or implementations.
Structural Design Patterns basically ease the design by identifying the relationships between entities.

3. Structural Design Patterns
Deal with objects delegating responsibilities to other objects.
This behavior results in a layered architecture of components with low degree of coupling.
Facilitate interobject communication when one object is not accessible to the other by normal means or when an object is not usable because of its incompatible interface.

4. Adapter or Wrapper Design Pattern

5. Adapter or Wrapper Design Pattern
Motivation
Laptop power supply to AC power supply Example

6. Adapter Design Pattern
Clients of a class access the services offered by the class through its interface.
Sometimes, an existing class may provide the functionality required by a client, but its interface may not be what the client expects.

7. Reasons for Incompatibility
This could happen due to various reasons such as the existing interface may be too detailed, or it
may lack in detail, or the terminology used by the interface may be different from what the client is looking for.

8. Goal
Keeping the client code intact we need to write a new class which will make use of services offered by the class.
Convert the services offered by class to the client in such a way that functionality will not be changed and the class will become reusable as shown in next slide.

13. Adapter Pattern Defined
“Adapter pattern convert the interface of the class into a form what client expects. Adapter let the classes work together which couldn’t otherwise due to incompatible interfaces.”

14. Issues in Adapter Design Pattern
Due to adapter class the changes are encapsulated within it and client is decoupled from the changes in the class.

15. Applicability – When to use
We want to use the existing class and its interface does not match with the one you need.
In case of reusable classes due Non-Compatible interfaces it is not possible to reuse them.

16. Class Diagram of Adapter Design Pattern

18. Flow of Application
Client call operations on Adaptor instance, which in return call adaptee opertions that carry out the request.

19. Type of Adapters
Object Adapters (Discussed till now)
Class Adapters

20. Class Diagram of Class Adapter

21. Example Data Structures in Java i-e Array, Vector Enumerators in Java
Enumerations

22. Enumerators in Java
public enum Day { SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY }

23. public class EnumTest { Day day; // defining Enumerator varaible public EnumTest(Day day) { this.day = day; } public void tellItLikeItIs() { switch (day) // accessing Enumerator Values { case MONDAY: System.out.println("Mondays are bad."); break; case FRIDAY: System.out.println("Fridays are better."); break; case SUNDAY: System.out.println("Weekends are best."); break; default: System.out.println("Midweek days are so-so."); break; } }

24. public static void main(String[] args) {// Access values of Enumerator EnumTest firstDay = new EnumTest(Day.MONDAY); firstDay.tellItLikeItIs(); EnumTest thirdDay = new EnumTest(Day.WEDNESDAY); thirdDay.tellItLikeItIs(); EnumTest fifthDay = new EnumTest(Day.FRIDAY); fifthDay.tellItLikeItIs(); EnumTest sixthDay = new EnumTest(Day.SATURDAY); sixthDay.tellItLikeItIs(); EnumTest seventhDay = new EnumTest(Day.SUNDAY); seventhDay.tellItLikeItIs(); }}