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package cgeo.geocaching.utils;
import java.util.LinkedHashSet;
import java.util.Set;
/**
* Synchronized implementation of the {@link ISubject} interface.
*
* @param <T>
* the kind of data to observe
*/
public class Subject<T> implements ISubject<T> {
/**
* Collection of observers.
*/
protected final Set<IObserver<? super T>> observers = new LinkedHashSet<IObserver<? super T>>();
@Override
public synchronized boolean addObserver(final IObserver<? super T> observer) {
final boolean added = observers.add(observer);
if (added && observers.size() == 1) {
onFirstObserver();
}
return added;
}
@Override
public synchronized boolean deleteObserver(final IObserver<? super T> observer) {
final boolean removed = observers.remove(observer);
if (removed && observers.isEmpty()) {
onLastObserver();
}
return removed;
}
@Override
public synchronized boolean notifyObservers(final T arg) {
final boolean nonEmpty = !observers.isEmpty();
for (final IObserver<? super T> observer : observers) {
observer.update(arg);
}
return nonEmpty;
}
@Override
public synchronized int sizeObservers() {
return observers.size();
}
@Override
public synchronized boolean clearObservers() {
final boolean nonEmpty = !observers.isEmpty();
for (final IObserver<? super T> observer : observers) {
deleteObserver(observer);
}
return nonEmpty;
}
/**
* Method called when the collection of observers goes from empty to non-empty.
* <p/>
* The default implementation does nothing and may be overwritten by child classes.
*/
protected void onFirstObserver() {
}
/**
* Method called when the collection of observers goes from non-empty to empty.
* <p/>
* The default implementation does nothing and may be overwritten by child classes.
*/
protected void onLastObserver() {
}
}
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