Observer Pattern

Last updated Nov 8, 2022 Edit Source

1. Tight coupling due to a 1-many dependency
2. We need a number of dependent objects to update automatically when one object changes state
3. We need an object to notify a number of other objects

**Pull

• 2-way communication: Subject sends a notification and the observer calls back for details explicitly (can be used for selective notification based on interest) **Push
• 1-way communication: Subject sends the detailed information whether the observer wants it or not (can be used for sending updates based on location etc.)

1. Abstracts coupling between Subject and Observer
2. Supports broadcast communication
3. Enable reusability of subjects and observers

1. Slower performance
2. Possible unnecessary complexity