The document discusses the observer pattern, which defines a one-to-many dependency between objects so that when one object changes state, all its dependent objects are notified and updated automatically. It provides an example of a stock system with a server as the subject and various client applications like a web app, mobile apps, and SMS alerts as observers. The observer pattern allows new observer types to be added without changing the subject.

1. Observer PatternAlbert Guojunyuo@gmail.com1

2. MotivationIntentImplementationApplicability & ExamplesAgenda2

3. Let's assume we have a stock system which provides data for several types of client. We want to have a client implemented as a web based application but in near future we need to add clients for mobile devices, Palm or Pocket PC, or to have a system to notify the users with sms alerts. Now it's simple to see what we need from the observer pattern: we need to separate the subject(stocks server) from it's observers(client applications) in such a way that adding new observer will be transparent for the server.Motivation3

4. Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.Intent4

5. Implementation5

6. 6Implementation – cont.

7. 7Applicability & Examples

8. 8Applicability & Examples – cont.

9. 9Applicability & Examples – cont.

10. 10Applicability & Examples – cont.

11. 11Applicability & Examples – cont.

12. 12Applicability & Examples – cont.

13. 13Applicability & Examples – cont.Email Subscriber: 《集中市場》三大法人賣超79億元，法說會績優股力抗國際崩跌SMS Subscriber: 《集中市場》三大法人賣超79億元，法說會績優股力抗國際崩跌RSS Subscriber: 《集中市場》三大法人賣超79億元，法說會績優股力抗國際崩跌----------------------------------------------------Email Subscriber: 台股盤後－鴻家軍登高力抗希臘債信危機 開低拉高力守8000關SMS Subscriber: 台股盤後－鴻家軍登高力抗希臘債信危機 開低拉高力守8000關RSS Subscriber: 台股盤後－鴻家軍登高力抗希臘債信危機 開低拉高力守8000關---------------------------------------------------