GJM: Design mode-Viewer mode

GJM: Observer mode

Video Address: http://www.imooc.com/learn/415

This course explains the application of the observer pattern in Java projects through a release and subscription case for weather forecasts. It mainly includes the structure of the observer pattern, the two implementations of the observer pattern, the model and the pull model, and when to use the observer pattern.

Observer Mode Combat

Structure and description of the Observer pattern

Learning Observer Pattern Generic code

Viewer mode

Recognize observer patterns

Two ways to implement: Push model and pull model

Using the observer implementations provided by Java

Briefly describe the pros and cons of observers

When to use Observer mode

The definition of the observer pattern

Defines a one-to-many dependency between objects. When the state of an object changes, all objects that depend on it are notified and automatically updated.

The observer receives the message The Observer observes the observer when the observer receives the message and performs its own logical processing

Structure of the Observer pattern

Subject Target Weather

SUBJECT Maintenance Observer List Subject has ADD Delete

Subject Execute Notify () = Subject Observer "Update ()" After receiving the target message

Structure diagram

subject{+add (Observer) + Delete (Observer) + Notify ()} <== ConcreteSubject [target message]

Subject =-+subject-> observer{+ Update ()} <== Concreteobserver interface logic implementation class

GJM: Design mode-Viewer mode