Observer Pattern in Java: Explanation & Practice

Problem summary

Create a NewsAgency (subject) that notifies NewsChannel observers when news is published.

Starter code

interface Observer {
    void update(String news);
}

// Implement NewsAgency and NewsChannel

public class Main {
    public static void main(String[] args) {
        NewsAgency agency = new NewsAgency();
        NewsChannel channel1 = new NewsChannel("CNN");
        NewsChannel channel2 = new NewsChannel("BBC");
        
        agency.subscribe(channel1);
        agency.subscribe(channel2);
        
        agency.publishNews("Breaking news!");
    }
}

Expected output and test cases

• All observers notified

  CNN received: Breaking news!
  BBC received: Breaking news!

Hints

1. Subject maintains list of observers
2. subscribe/unsubscribe methods
3. publishNews iterates and calls update on each

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