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POJava Listener inheritance
 

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    <p>I have a java class which fires custom java events. The structure of the code is the following:</p> <pre><code>public class AEvent extends EventObject { ... } public interface AListener extends EventListener { public void event1(AEvent event); } public class A { public synchronized void addAListener(AListener l) { .. } public synchronized void removeAListener(AListener l) { .. } protected void fireAListenerEvent1(AEvent event) { .. } } </code></pre> <p>Everything works correctly, but I'd like to create a new subclass of A (call it B), which may fire a new event. I'm thinking of the following modification:</p> <pre><code>public class BEvent extends AEvent { ... } public interface BListener extends AListener { public void event2(BEvent event); } public class B extends A { public synchronized void addBListener(BListener l) { .. } public synchronized void removeBListener(BListener l) { .. } protected void fireBListenerEvent2(AEvent event) { .. } } </code></pre> <p>Is this the correct approach? I was searching the web for examples, but couldn't find any.</p> <p>There are a few things I don't like in this solution:</p> <ol> <li><code>BListener</code> has two methods one uses <code>AEvent</code> the other uses <code>BEvent</code> as a parameter.</li> <li><code>B</code> class both has <code>addAListener</code> and <code>addBListener</code> methods. Should I hide addAListener with private keyword? <strong>[UPDATE: it's not possible to hide with private keyword]</strong></li> <li>Similar problem with <code>fireAListenerEvent1</code> and <code>fireBListenerEvent1</code> methods.</li> </ol> <p>I'm using Java version 1.5.</p>
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    1. COCould you expand a bit on your motives for this design? Why does matter that B extend A, in what kind of situations are all this stuff going to be used? Otherwise uzhin's approach seems to be pointing in a right direction.
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    2. COB adds new functionality to class A. It means that the event fired by A (event1) is a valid event for class B. Because of the new functionality a new event (event2) is also valid for B. I'd like to handle the two events (event1+event2) together since they are related.
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    3. COSide note: a ConcurrentModificationException can occur in the fireXXX methods unless you synchronize those as well (expensive!). For typical use cases, it's faster and less error-prone to use java.util.concurrent.CopyOnWriteArrayList for your listener list so that synchronization is unnecessary.
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