We use simple examples and diagrams to describe the concept of observer pattern. We also give a simple implementation of the observer pattern in Java.
What is Observer Pattern
The observer pattern defines a one-to-many relationship between two kinds of objects. The one side is called Subject, which maintains a list of Objects (called observers), and automatically notify each of the observers if something interesting happens.
The definition of the Observer pattern provided in the GoF book, Design Patterns: Elements of Reusable Object-Oriented Software, is:
“One or more observers are interested in the state of a subject and register their interest with the subject by attaching themselves.[Read More...]