The Observer pattern defines a one-to-many relationship between objects. When the state of one object (the subject or observable) changes, all its dependents (observers) are automatically notified and updated. This pattern encourages loose coupling between the subject and its observers and is especially helpful for implementing distributed event-handling systems.

Imagine a weather station that gathers data and has various display elements that must show this data, such as a current condition display, a statistics display, and a forecast display