javafx.beans.Observable Maven / Gradle / Ivy
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package javafx.beans;
import java.util.Objects;
import javafx.util.Subscription;
/**
* An {@code Observable} is an entity that wraps content and allows to
* observe the content for invalidations.
*
* An implementation of {@code Observable} may support lazy evaluation,
* which means that the content is not immediately recomputed after changes, but
* lazily the next time it is requested. All bindings and properties in
* this library support lazy evaluation.
*
* Implementations of this class should strive to generate as few events as
* possible to avoid wasting too much time in event handlers. Implementations in
* this library mark themselves as invalid when the first invalidation event
* occurs. They do not generate anymore invalidation events until their value is
* recomputed and valid again.
*
* @see javafx.beans.value.ObservableValue
* @see javafx.collections.ObservableList
* @see javafx.collections.ObservableMap
*
*
* @since JavaFX 2.0
*/
public interface Observable {
/**
* Adds an {@link InvalidationListener} which will be notified whenever the
* {@code Observable} becomes invalid. If the same
* listener is added more than once, then it will be notified more than
* once. That is, no check is made to ensure uniqueness.
*
* Note that the same actual {@code InvalidationListener} instance may be
* safely registered for different {@code Observables}.
*
* The {@code Observable} stores a strong reference to the listener
* which will prevent the listener from being garbage collected and may
* result in a memory leak. It is recommended to either unregister a
* listener by calling {@link #removeListener(InvalidationListener)
* removeListener} after use or to use an instance of
* {@link WeakInvalidationListener} avoid this situation.
*
* @see #removeListener(InvalidationListener)
*
* @param listener
* The listener to register
* @throws NullPointerException
* if the listener is null
*/
void addListener(InvalidationListener listener);
/**
* Removes the given listener from the list of listeners, that are notified
* whenever the value of the {@code Observable} becomes invalid.
*
* If the given listener has not been previously registered (i.e. it was
* never added) then this method call is a no-op. If it had been previously
* added then it will be removed. If it had been added more than once, then
* only the first occurrence will be removed.
*
* @see #addListener(InvalidationListener)
*
* @param listener
* The listener to remove
* @throws NullPointerException
* if the listener is null
*/
void removeListener(InvalidationListener listener);
/**
* Creates a {@code Subscription} on this {@code Observable} which calls
* {@code invalidationSubscriber} whenever it becomes invalid. The provided
* subscriber is akin to an {@code InvalidationListener} without the
* {@code Observable} parameter. If the same subscriber is subscribed more
* than once, then it will be notified more than once. That is, no check is
* made to ensure uniqueness.
*
* Note that the same subscriber instance may be safely subscribed for
* different {@code Observables}.
*
* Also note that when subscribing on an {@code Observable} with a longer
* lifecycle than the subscriber, the subscriber must be unsubscribed
* when no longer needed as the subscription will otherwise keep the subscriber
* from being garbage collected.
*
* @param invalidationSubscriber a {@code Runnable} to call whenever this
* value becomes invalid, cannot be {@code null}
* @return a {@code Subscription} which can be used to cancel this
* subscription, never {@code null}
* @throws NullPointerException if the subscriber is {@code null}
* @see #addListener(InvalidationListener)
* @since 21
*/
default Subscription subscribe(Runnable invalidationSubscriber) {
Objects.requireNonNull(invalidationSubscriber, "invalidationSubscriber cannot be null");
InvalidationListener listener = obs -> invalidationSubscriber.run();
addListener(listener);
return () -> removeListener(listener);
}
}