Observer

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

Usage          High

UML class diagram

A visualization of the classes and objects participating in this pattern.

Sample code

This structural code demonstrates the Observer pattern in which registered objects are notified of and updated with a state change.

Output

See also

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• Common Design Patterns
• Design Guidelines
• Documentation