# What is Observer Design Pattern 
The observer pattern is a Behavioral design pattern in which an object, called the subject, maintains a list of its dependents, called observers, and notifies them automatically of any state changes or updates.

## Diagram
![Diagram](https://github.com/premaseem/DesignPatternsJava9/blob/observer-pattern/diagrams/Observer-Pattern-class-diagram.png "Diagram")

![Diagram](https://github.com/premaseem/DesignPatternsJava9/blob/observer-pattern/diagrams/Observer-Design-Pattern-generic.jpeg "Diagram")

![Diagram](https://github.com/premaseem/DesignPatternsJava9/blob/observer-pattern/diagrams/ObserverSequenceDiagram.png "Diagram")

# When to use Observer Design Pattern 
* Heavy used in  "event driven" application
* It is suitable for any scenario that requires push-based notification.

### Learn Design Patterns with Java by Aseem Jain
This repository contains working project code used in video Course by Packt Publication with title "Learn Design Patterns with Java " authored by "Aseem Jain".

### Course link: 
https://www.packtpub.com/application-development/learn-design-patterns-java-9-video

### ![ http://in.linkedin.com/in/premaseem](https://github.com/premaseem/DesignPatternsJava9/blob/master/linkedin.png "http://in.linkedin.com/in/premaseem") Profile:  http://in.linkedin.com/in/premaseem

### Authors blog on design patterns:
https://premaseem.wordpress.com/category/computers/design-patterns/

### Software Design pattern community face book page:
https://www.facebook.com/DesignPatternGuru/

### Note: 
* This code base will work on Java 9 and above versions. 
* `diagrams` folders carry UML diagrams.
* `pattern` folder has code of primary example. 
* `patternBonus` folder has code of secondary or bonus example.