Two Levels Observer

import java.util.ArrayList;

/**
 *
 * @author LeFex
 */
public class Test {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        IObservable observable = new ConcreteObservable();
        IObserver observer = new ConcreteObserver(observable);
        observable.register(observer);
        ConcreteObserverAndObservable middle = new ConcreteObserverAndObservable(observable);
        observable.register(middle);
        IObserver secondHandObserver = new ConcreteObserver(middle);
        middle.register(secondHandObserver);

        observable.doStuff("HELLO");
        observable.updateObservers();
    }

}

interface IObserver{

    public void update();

}

interface IObservable{

    public void updateObservers();
    public void register(IObserver obs);
    public void unRegister(IObserver obs);
    public String getData();
    public void doStuff(String stuff);
}

class ConcreteObservable implements IObservable{

    private ArrayList<IObserver> mObservers = new ArrayList<>();
    private String mData = "";

    @Override
    public void updateObservers() {
        for(IObserver o : mObservers){
            o.update();
        }
    }

    @Override
    public void register(IObserver obs) {
        mObservers.add(obs);
    }

    @Override
    public void unRegister(IObserver obs) {
        mObservers.remove(obs);
    }

    @Override
    public String getData() {
        return mData;
        }

    @Override
    public void doStuff(String stuff) {
        mData = stuff;
    }
}

class ConcreteObserver implements IObserver{

    private IObservable mSubject;

    public ConcreteObserver(IObservable subject){
        mSubject = subject;
    }

    @Override
    public void update() {
        String data = mSubject.getData();
        System.out.println(data);
    }

}

class ConcreteObserverAndObservable implements IObservable, IObserver{

    private ArrayList<IObserver> mObservers = new ArrayList<>();
    private String mData = "";
    private IObservable mSubject;

    public ConcreteObserverAndObservable(IObservable subject){
         mSubject = subject;
    }

    @Override
    public void updateObservers() {
        for(IObserver o : mObservers){
            o.update();
        }
    }

    @Override
    public void register(IObserver obs) {
        mObservers.add(obs);
    }

    @Override
    public void unRegister(IObserver obs) {
        mObservers.remove(obs);
    }

    @Override
    public String getData() {
        return mData;
    }

    @Override
    public void update() {
        String temp = mSubject.getData();
        mData = temp + " " + temp;
        updateObservers();
    }

    @Override
    public void doStuff(String stuff) {
        mData = stuff;
    }

}