Observer pattern - Software Design Pattern | Using Lambda Expression & Method Reference

Observer pattern - Software Design Pattern
- Using Lambda Expression & Method Reference
- Define a one-to-many dependency between objects
- An object, named the subject, maintains a list of its dependents, called observers when a subject changes state, all registered observers are notified and updated automatically (and probably asynchronously)
- Distributed event handling systems in event driven
- Publish-subscribe model
- Reactive Streams - Spring Project Reactor - Flux, Mono, RxJava - Observable, observer, Kotlin - Flow

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