Observer vs Pub-sub pattern

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• In the Observer pattern, the Observers are aware of the Subject, also the Subject maintains a record of the Observers. Whereas, in Publisher/Subscriber, publishers and subscribers don’t need to know each other. They simply communicate with the help of message queues or broker.
• In Publisher/Subscriber pattern, components are loosely coupled as opposed to Observer pattern.
• Observer pattern is mostly implemented in a synchronous way, i.e. the Subject calls the appropriate method of all its observers when some event occurs. The Publisher/Subscriber pattern is mostly implemented in an asynchronous way (using message queue).
• Observer pattern need to be implemented in a single application address space. On the other hand, Publisher/Subscriber pattern is more of a cross application pattern.

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Use patterns where they are natural, do not try to use them anyway. Design Patterns is a great tool to build great software. Use them wisely, do not abuse them.