Observer Pattern

The Observer Pattern defines a one-to-many dependency between objects so that when one object changes state, all of its dependents are notified and updated automatically.


Important point:

  • Subject maintains a collection of objects called observers.
  • When the subject changes, it notifies the observers.

  • Observers can be added or removed from the collection of observers in the subject.

  • The Subject only notifies that its state has changes, it does not pass any information. Observers have to change their own state to reflect the change.

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