Observer Design Pattern Tutorial with Java Coding for Beginners | Observer Pattern Explained

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. The observer pattern is also known as Dependents or Publish-Subscribe. Observer pattern is used when there is one-to-many relationship between objects such as if one object is modified, its dependent objects are to be notified automatically.

** Problem and Solution **
Imagine a scenario of Customers and a Store. The customer is very interested in a particular brand of product (let say iPhone) which should become available in the store very soon. The customer could visit the store every day and check product availability. But while the product is still on the way, most of these trips would be pointless. On the other hand, if store sends tons of emails to all customers each time a new product becomes available which might be considered spam. So, we have a problem here. Either the customer wasting time checking product availability or the store wastes resources notifying the wrong customers. Solution to this problem is “Observer Design Pattern”. The Observer pattern suggests that you add a subscription mechanism to the publisher class so individual objects can subscribe to or unsubscribe from a stream of events coming from that publisher.

** Where to use Observer Design Pattern **
1. Use the Observer pattern when an object wants to publish information and many objects will need to receive that information.
2. Use the Observer pattern when changes to the state of one object may require changing other objects, and the actual set of objects is unknown beforehand or changes dynamically.
3. Use the Observer pattern when some objects in your app must observe others, but only for a limited time or in specific cases.
** Advantages of Observer Design Pattern **
1. Observer Design Pattern makes for a loose coupling between publisher and subscriber as the publisher does not need to know who or how many subscribers there will be.
2. Observer Design Pattern supports Open/Closed Principle. You can introduce new subscriber classes without having to change the publisher’s code.
3. Using Observer Design Pattern You can establish relations between objects at runtime.

** Chapter Timestamps **
0:00 Welcome to Observer Design Pattern
0:23 Recap of Strategy Design Pattern
1:30 Introduction of Observer Design Pattern
2:04 Real world example of Observer Design Pattern
3:51 Java coding example of Observer Design Pattern
8:30 Usage of Observer Design Pattern
9:11 Advantages of Observer Design Pattern
9:47 Summary of Observer Design Pattern
10:27 Next video on Template Design Pattern

#observerpattern #observerdesignpattern #javadesignpatterns

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Strategy Design Pattern https://youtu.be/L98hHGPp8VY

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** References ** https://www.tutorialspoint.com/design_pattern/design_pattern_overview.htm

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