/*
 * Copyright (c) 2011, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package javafx.beans;


An Observable is an entity that wraps content and allows to observe the content for invalidations. 
 An implementation of 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 Also:
ObservableValue
ObservableList
ObservableMap
Since:
JavaFX 2.0/**
 * An {@code Observable} is an entity that wraps content and allows to
 * observe the content for invalidations.
 * <p>
 * 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.
 * <p>
 * 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 InvalidationListener which will be notified whenever the 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 InvalidationListener instance may be safely registered for different Observables. 
 The 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 
removeListener after use or to use an instance of WeakInvalidationListener avoid this situation. 
Params:
listener – 
           The listener to register
Throws:
NullPointerException – 
            if the listener is null
See Also:
removeListener(InvalidationListener)/**
     * 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.
     * <p>
     * Note that the same actual {@code InvalidationListener} instance may be
     * safely registered for different {@code Observables}.
     * <p>
     * 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 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.
Params:
listener – 
           The listener to remove
Throws:
NullPointerException – 
            if the listener is null
See Also:
addListener(InvalidationListener)/**
     * Removes the given listener from the list of listeners, that are notified
     * whenever the value of the {@code Observable} becomes invalid.
     * <p>
     * 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);

}