1. DESIGN PATTERNS

2. s/w design
 What is s/w design?
 Bad design?
 Good design?
 How to approach?

3. Design Patterns
 What ???
&
 Why???

4. Patterns of our concern
OBSERVER PATTERN
IOC PATTERN

5. OBSERVER PATTERN

6. Observer pattern
 One to many dependency between objects.
 When an object changes state , all its
dependencies are notified and updated.

7. Example
Participants
Subject(stock)
• Knows the list of investors.
• Provides methods for attaching , detaching and notifying
observers.
Concrete subject(RM)
• Stores the state of interest to observers.
• Notifies observer when state changes.

8. Observer
• Interface for objects that is to be notified with the changes of
subject.
Concrete observer
• Update the observer with the subject.
• Maintains a reference to the concrete subject object.

9. IOC

10. DI principle
• High level module should not depend on low level
modules . Both should depend on abstraction.
• Abstraction should not depend on details . Details
should depend on abstraction.

11. Dependency inversion
principle
IOC
Service Locator
Dependency
Injection

12. IOC
• A design pattern based on DIP
• Inverting the control so that lower module does not control the interface
and object creation.

13. DI
• Specialization of IOC.
• Helps to make loosely coupled code.
• Increase extensibility and maintainability.
• The Dependency Injection pattern uses a builder
object to initialize objects and provide the required
dependencies to the object means it allows you to
"inject" a dependency from outside the class.

14. Service Locator
• The Service Locator pattern introduces a locator
object that objects is used to resolve dependencies
means it allows you to "resolve" a dependency
within a class.

15. References
•
http://satoricode.net/2011/10/01/UnderstandingTheBenefitsOfADependencyInjec
tionContainerIOC.aspx
•
http://www.oodesign.com/dependency-inversion-principle.html
•
http://www.dofactory.com/Patterns/Patterns.aspx
•
http://www.dotnet-tricks.com/Tutorial/dependencyinjection/bSVa100413Understanding-Inversion-of-Control,-Dependency-Injection-and-ServiceLocator.html
•
http://martinfowler.com/articles/injection.html

16. THANK YOU