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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
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 * 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.
 *
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package javafx.beans.binding;

import javafx.beans.InvalidationListener;
import javafx.beans.Observable;
import javafx.beans.value.ChangeListener;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;

import com.sun.javafx.binding.BindingHelperObserver;
import com.sun.javafx.binding.ExpressionHelper;

/**
 * Base class that provides most of the functionality needed to implement a
 * {@link Binding} of an {@code Object}.
 * <p>
 * {@code ObjectBinding} provides a simple invalidation-scheme. An extending
 * class can register dependencies by calling {@link #bind(Observable...)}.
 * If One of the registered dependencies becomes invalid, this
 * {@code ObjectBinding} is marked as invalid. With
 * {@link #unbind(Observable...)} listening to dependencies can be stopped.
 * <p>
 * To provide a concrete implementation of this class, the method
 * {@link #computeValue()} has to be implemented to calculate the value of this
 * binding based on the current state of the dependencies. It is called when
 * {@link #get()} is called for an invalid binding.
 * <p>
 * See {@link DoubleBinding} for an example how this base class can be extended.
 *
 * @see Binding
 * @see javafx.beans.binding.ObjectExpression
 *
 * @param <T>
 *            the type of the wrapped {@code Object}
 * @since JavaFX 2.0
 */
public abstract class ObjectBinding<T> extends ObjectExpression<T> implements
        Binding<T> {

    private T value;
    private boolean valid = false;
    private BindingHelperObserver observer;
    private ExpressionHelper<T> helper = null;

    @Override
    public void addListener(InvalidationListener listener) {
        helper = ExpressionHelper.addListener(helper, this, listener);
    }

    @Override
    public void removeListener(InvalidationListener listener) {
        helper = ExpressionHelper.removeListener(helper, listener);
    }

    @Override
    public void addListener(ChangeListener<? super T> listener) {
        helper = ExpressionHelper.addListener(helper, this, listener);
    }

    @Override
    public void removeListener(ChangeListener<? super T> listener) {
        helper = ExpressionHelper.removeListener(helper, listener);
    }

    /**
     * Start observing the dependencies for changes. If the value of one of the
     * dependencies changes, the binding is marked as invalid.
     *
     * @param dependencies
     *            the dependencies to observe
     */
    protected final void bind(Observable... dependencies) {
        if ((dependencies != null) && (dependencies.length > 0)) {
            if (observer == null) {
                observer = new BindingHelperObserver(this);
            }
            for (final Observable dep : dependencies) {
                dep.addListener(observer);
            }
        }
    }

    /**
     * Stop observing the dependencies for changes.
     *
     * @param dependencies
     *            the dependencies to stop observing
     */
    protected final void unbind(Observable... dependencies) {
        if (observer != null) {
            for (final Observable dep : dependencies) {
                dep.removeListener(observer);
            }
            observer = null;
        }
    }

    /**
     * A default implementation of {@code dispose()} that is empty.
     */
    @Override
    public void dispose() {
    }

    /**
     * A default implementation of {@code getDependencies()} that returns an
     * empty {@link javafx.collections.ObservableList}.
     *
     * @return an empty {@code ObservableList}
     */
    @Override
    public ObservableList<?> getDependencies() {
        return FXCollections.emptyObservableList();
    }

    /**
     * Returns the result of {@link #computeValue()}. The method
     * {@code computeValue()} is only called if the binding is invalid. The
     * result is cached and returned if the binding did not become invalid since
     * the last call of {@code get()}.
     *
     * @return the current value
     */
    @Override
    public final T get() {
        if (!valid) {
            value = computeValue();
            valid = true;
        }
        return value;
    }

    /**
     * The method onInvalidating() can be overridden by extending classes to
     * react, if this binding becomes invalid. The default implementation is
     * empty.
     */
    protected void onInvalidating() {
    }

    @Override
    public final void invalidate() {
        if (valid) {
            valid = false;
            onInvalidating();
            ExpressionHelper.fireValueChangedEvent(helper);
        }
    }

    @Override
    public final boolean isValid() {
        return valid;
    }

    /**
     * Calculates the current value of this binding.
     * <p>
     * Classes extending {@code ObjectBinding} have to provide an implementation
     * of {@code computeValue}.
     *
     * @return the current value
     */
    protected abstract T computeValue();

    /**
     * Returns a string representation of this {@code ObjectBinding} object.
     * @return a string representation of this {@code ObjectBinding} object.
     */
    @Override
    public String toString() {
        return valid ? "ObjectBinding [value: " + get() + "]"
                : "ObjectBinding [invalid]";
    }
}
