Question

The code below was taken from another SO post, I was wondering is there a better way of writing this code, because its kind of ugly to have a loop that notifies all the listener at the end of every implemented method. If this is silly forgive me, I am new to Java.

Note: I will be implementing more than one method in the interface, I will have 5 methods implemented:

import java.util.*;

interface HelloListener {
    public void someoneSaidHello();
}


class Initiater {
    List<HelloListener> listeners = new ArrayList<HelloListener>();

    public void addListener(HelloListener toAdd) {
        listeners.add(toAdd);
    }

    public void sayHello() {
        System.out.println("Hello!!");

        // Notify everybody that may be interested.
        for (HelloListener hl : listeners)
            hl.someoneSaidHello();
    }
}


class Responder implements HelloListener {
    @Override
    public void someoneSaidHello() {
        System.out.println("Hello there...");
    }
}

Answer 1

When I implemented the Observer pattern as a student, I made it as an abstract class:

import java.util.ArrayList;

/**
 * The observer pattern.
 * @author jiman 
 */
public abstract class Observed {

    private ArrayList<Observer> observers;

    public Observed() { views = new ArrayList<Observer>(); }

    public void registerObserver(Observer o) { observers.add(o); }

    public void removeObserver(Observer o) { observers.remove(o); }

    // call this method upon a mutation of the state of this object
    public void notifyObservers() { for (Observer o : observers) o.update(); }

}

Observers will inherit from this interface and write their own update methods.

public interface Observer {

    public void update();

}