Design Pattern Slide 03aaaaaaaaaaaaaaaaaaa.pptx

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1. Design Pattern Behavioral patterns Computer Science Faculty Network Engineering Department Slide:- 03 Year:- 2024

2. Contents Behavioral patterns Types of Behavior Patterns Observer Pattern When to use Observer Method

3. Behavioral patterns In software engineering, behavioral design patterns are design patterns that identify common communication patterns between objects and realize these patterns. By doing so, these patterns increase flexibility in carrying out this communication.

4. Types of Behavior Patterns Observer A way of notifying change to a number of classes Chain of responsibility A way of passing a request between a chain of objects Command Encapsulate a command request as an object Interpreter A way to include language elements in a program

5. Types of Behavior Patterns Iterator Sequentially access the elements of a collection Mediator Defines simplified communication between classes Memento Capture and restore an object's internal state Null Object

6. Types of Behavior Patterns State Alter an object's behavior when its state changes Strategy Encapsulates an algorithm inside a class Template method Defer the exact steps of an algorithm to a subclass Visitor Defines a new operation to a class without change

7. Observer Pattern Observer  is a behavioral design pattern that lets you define a subscription mechanism to notify multiple objects about any events that happen to the object they’re observing.

8. Observer Pattern An Observer Pattern says that "just define a one-to-one dependency so that when one object changes state, all its dependents are notified and updated automatically". The observer pattern is also known as Dependents or Publish-Subscribe.

9. Continue… There are three recurring themes in these patterns: Behavioral class patterns use inheritance to distribute behavior between classes. Behavioral object patterns use object composition rather than inheritance. Behavioral object patterns are concerned with encapsulating behavior in an object and delegating requests to it.

10. Benefits and Usages It describes the coupling between the objects and the observer. It provides the support for broadcast-type communication. When the change of a state in one object must be reflected in another object without keeping the objects tight coupled. When the framework we writes and needs to be enhanced in future with new observers with minimal chamges .

11. When to use Observer Method Use the Observer pattern in any of the following situations: When an abstraction has two aspects, one dependent on the other. Encapsulating these aspects in separate objects lets you vary and reuse them independently. When a change to one object requires changing others, and you don’t know how many objects need to be changed. When an object should be able to notify other objects without making assumptions about who these objects are.In other words, you don’t want these objects tightly coupled.

12. UML for Observer Pattern