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package javafx.collections;

import javafx.beans.NamedArg;
import javafx.beans.WeakListener;

import java.lang.ref.WeakReference;

A WeakSetChangeListener can be used, if an ObservableSet should only maintain a weak reference to the listener. This helps to avoid memory leaks, that can occur if observers are not unregistered from observed objects after use. 
 WeakSetChangeListener are created by passing in the original SetChangeListener. The WeakSetChangeListener should then be registered to listen for changes of the observed object. 
 Note: You have to keep a reference to the SetChangeListener, that was passed in as long as it is in use, otherwise it will be garbage collected to soon. 
Type parameters:
<E> – 
           The type of the observed value
See Also:
SetChangeListener
ObservableSet
WeakListener
Since:
JavaFX 2.1/**
 * A {@code WeakSetChangeListener} can be used, if an {@link javafx.collections.ObservableSet}
 * should only maintain a weak reference to the listener. This helps to avoid
 * memory leaks, that can occur if observers are not unregistered from observed
 * objects after use.
 * <p>
 * {@code WeakSetChangeListener} are created by passing in the original
 * {@link SetChangeListener}. The {@code WeakSetChangeListener} should then be
 * registered to listen for changes of the observed object.
 * <p>
 * Note: You have to keep a reference to the {@code SetChangeListener}, that
 * was passed in as long as it is in use, otherwise it will be garbage collected
 * to soon.
 *
 * @see SetChangeListener
 * @see ObservableSet
 * @see javafx.beans.WeakListener
 *
 * @param <E>
 *            The type of the observed value
 *
 * @since JavaFX 2.1
 */
public final class WeakSetChangeListener<E> implements SetChangeListener<E>, WeakListener {

    private final WeakReference<SetChangeListener<E>> ref;

    
The constructor of WeakSetChangeListener. 
Params:
listener – 
           The original listener that should be notified/**
     * The constructor of {@code WeakSetChangeListener}.
     *
     * @param listener
     *            The original listener that should be notified
     */
    public WeakSetChangeListener(@NamedArg("listener") SetChangeListener<E> listener) {
        if (listener == null) {
            throw new NullPointerException("Listener must be specified.");
        }
        this.ref = new WeakReference<SetChangeListener<E>>(listener);
    }

    
{@inheritDoc}
/**
     * {@inheritDoc}
     */
    @Override
    public boolean wasGarbageCollected() {
        return (ref.get() == null);
    }

    
{@inheritDoc}
/**
     * {@inheritDoc}
     */
    @Override
    public void onChanged(Change<? extends E> change) {
        final SetChangeListener<E> listener = ref.get();
        if (listener != null) {
            listener.onChanged(change);
        } else {
            // The weakly reference listener has been garbage collected,
            // so this WeakListener will now unhook itself from the
            // source bean
            change.getSet().removeListener(this);
        }
    }
}