javafx.beans.value.WeakChangeListener Maven / Gradle / Ivy
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* accompanied this code).
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package javafx.beans.value;
import javafx.beans.NamedArg;
import javafx.beans.WeakListener;
import java.lang.ref.WeakReference;
/**
* A {@code WeakChangeListener} can be used if an {@link ObservableValue}
* should only maintain a weak reference to the listener. This helps to avoid
* memory leaks which can occur if observers are not unregistered from observed
* objects after use.
*
* {@code WeakChangeListener} instances are created by passing in the original
* {@link ChangeListener}. The {@code WeakChangeListener} should then be
* registered to listen for changes of the observed object.
*
* Note: You have to keep a reference to the {@code ChangeListener} that
* was passed in for as long as it is in use, otherwise it will be garbage collected
* too soon.
*
* @see ChangeListener
* @see ObservableValue
*
* @param The type of the observed value
*
* @since JavaFX 2.0
*/
public final class WeakChangeListener implements ChangeListener, WeakListener {
private final WeakReference> ref;
/**
* The constructor of {@code WeakChangeListener}.
*
* @param listener The original listener that should be notified
*/
public WeakChangeListener(@NamedArg("listener") ChangeListener listener) {
if (listener == null) {
throw new NullPointerException("Listener must be specified.");
}
this.ref = new WeakReference>(listener);
}
/**
* {@inheritDoc}
*/
@Override
public boolean wasGarbageCollected() {
return (ref.get() == null);
}
/**
* {@inheritDoc}
*/
@Override
public void changed(ObservableValue observable, T oldValue,
T newValue) {
ChangeListener listener = ref.get();
if (listener != null) {
listener.changed(observable, oldValue, newValue);
} else {
// The weakly reference listener has been garbage collected,
// so this WeakListener will now unhook itself from the
// source bean
observable.removeListener(this);
}
}
}