Uncle Bob's Agile Development Corner
OBSERVER—Evolving into a pattern, Part 2
by Robert C. Martin
Listing 9.

import java.util.*;

public class Subject
    private Vector itsObservers = new Vector();

    protected void notifyObservers()
        Iterator i = itsObservers.iterator();
        while (i.hasNext())
            Observer observer = (Observer);

    public void registerObserver(Observer observer)

About the Author

Robert C. Martin is president of Object Mentor Inc., a firm that offers high-level, OO software design consulting, training, and development services. He is the author of Designing Object Oriented C++ Applications Using the Booch Method. He can be contacted at


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