Design Patterns : Observer Pattern

Article by Haneez Haroon    Comments Off  

Definition

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

Applicability

Use Observer pattern when

• An abstraction has two aspects, one dependent on the other. Encapsulating these aspects in separate objects let you vary and reuse them independently.
• A change to one object requires changing others, and you don’t know how many objects need to be changed.
• An object should be able to notify other objects without making assumption about who these objects are. In other words, you don’t want these objects tightly coupled.

Diagram

[Design Patterns - Gamma, et al, 1995]