Benefits

• Loose Coupling: Subjects and observers are decoupled. They can interact without needing to know much about each other, promoting easier maintenance and scalability.
• Flexibility and Extensibility: It allows for dynamic relationships between objects. New observers can be added or removed without modifying the subject or other observers.
• Event Handling: Facilitates event-driven architectures where actions in one part of the application trigger responses in other parts, making it suitable for reactive programming.
• Consistency: Ensures that dependent objects (observers) are always updated with the latest state of the subject, maintaining consistency across the application.
• Modular Design: Encourages a modular design approach where subjects and observers can be developed and tested independently, promoting code reusability.
• Reduction of Spaghetti Code: Helps in avoiding tangled dependencies and spaghetti code by providing a clear separation of concerns between components.
• Support for Broadcast Communication: Enables efficient communication where multiple objects need to react to changes in a single object's state, reducing redundant code.
• Ease of Maintenance: Enhances code maintainability by reducing the likelihood of side effects when making changes to one part of the system.

Structure

• Subject: Maintains a list of observers.Defines methods to set and get the state that observers are interested in.
• Observer: Defines an interface or abstract class with a method. Concrete observers implement this interface to receive updates from the subject.
• Concrete Subject: Implements the subject interface. Maintains the state of interest that observers monitor. Sends notifications to observers when the state changes.
• Concrete Observer: Implements the observer interface. Registers itself with the subject to receive notifications. Defines actions to take in response to updates received from the subject.
• Client: Initiates the creation of subjects and observers. Configures how observers are attached to subjects and when they should be notified.