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Observer

📎 Observer pattern is used when there is one-to-many relationship between objects such as if one object's state is modified, its depenedent objects are to be notified automatically.

The same principal as the" Publish-Subscribe"

Diagram​

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Example : Weather station (we should be notifed everytime the weather change)​

Our job is to create an app that uses the WeatherData object (which takes dtaa from a sensor) to update three displays elements

  • Current conditions (temperature/humidity/pressure)
  • Weather statistics
  • forecast

these three are our observer concrete classes

so the weather data class should notify all the observers each time it has a new state

notify method in weatherData calls the update method in observers classes

the concrete observer is add as w subscriber to the subject = register to a subject

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Implementation​

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