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Observer Pattern

What is the Observer Pattern?

The Observer Pattern is a behavioral design pattern that lets you define a subscription mechanism to notify multiple objects about any events that happen to the object they're observing.

Implementation in This Project

This example demonstrates the Observer pattern by using a subject with multiple observers:

  • Subject: The object being observed.
  • Observer: Abstract observer class.
  • BinaryObserver, OctalObserver, HexaObserver: Concrete observers.

Class Diagram

flowchart TD
    A["App.java"] --> B["Subject"]
    B --> C["Observer (abstract)"]
    C --> D["BinaryObserver"]
    C --> E["OctalObserver"]
    C --> F["HexaObserver"]
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Example Usage

Subject subject = new Subject();

new HexaObserver(subject);
new OctalObserver(subject);
new BinaryObserver(subject);

System.out.println("First state change: 15");
subject.setState(15);
System.out.println("Second state change: 10");
subject.setState(10);

When to Use

  • When you want to notify multiple objects about changes in another object's state.
  • When you want to implement a one-to-many dependency between objects.