Says I am overriding final method but I can't find final

Question

I am trying to implement a Observer Pattern on Java. It won't compile because notifyAll() seems to be the problem here; Cannot override the final method from Object but I haven't put any 'final' nor 'static' in the code. What am I doing wrong here?

import java.util.ArrayList;
import java.util.List;

interface Observer {
    void update();
}

interface Subject {
    void registerObserver(Observer o);
    void deregisterObserver(Observer o);    
    void notifyAll();    
}

// Concrete Class
class User implements Observer {
    @Override
    public void update() {
        System.out.println("Donald Trump just tweeted, you know");
    }
}

// Concrete Class
class realDonaldTrump implements Subject {
    private boolean hasTweeted = false;
    private ArrayList<Observer> followers = new ArrayList<Observer>();

    public boolean hasTweetedIn24Hours() {
        return hasTweeted;
    }

    public void donaldTweets(boolean hasTweeted) {
        this.hasTweeted = hasTweeted;
        notifyAll();
    }


    @Override
    public void registerObserver(Observer o) {
        followers.add(o);
    }

    @Override
    public void deregisterObserver(Observer o) {
        followers.remove(o);
    }

    @Override
    public void notifyAll() {
        for (Observer o: followers)
            o.update();
    }

}

public class ObserverPatternDemo {
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        System.out.println("Hello World");
        System.out.println("Observer Pattern Demo");
        realDonaldTrump tweeterAcc = new realDonaldTrump();

    }

}

Answer 1

By default all classes extend the Object class which has a final method named notifyAll() . Since the method is final, it cannot be overridden in your class.

 public final native void notifyAll(); // in Object class