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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 Binding of a double value. 
 DoubleBinding provides a simple invalidation-scheme. An extending class can register dependencies by calling bind(Observable...). If One of the registered dependencies becomes invalid, this DoubleBinding is marked as invalid. With unbind(Observable...) listening to dependencies can be stopped. 
 To provide a concrete implementation of this class, the method computeValue() has to be implemented to calculate the value of this binding based on the current state of the dependencies. It is called when get() is called for an invalid binding. 
 Below is a simple example of a DoubleBinding calculating the square- root of a ObservableNumberValue moo. 

final ObservableDoubleValue moo = ...;
DoubleBinding foo = new DoubleBinding() {
    {
        super.bind(moo);
    }
    @Override
    protected double computeValue() {
        return Math.sqrt(moo.getValue());
    }
};

 Following is the same example with implementations for the optional methods Binding.getDependencies() and Binding.dispose(). 

final ObservableDoubleValue moo = ...;
DoubleBinding foo = new DoubleBinding() {
    {
        super.bind(moo);
    }
    @Override
    protected double computeValue() {
        return Math.sqrt(moo.getValue());
    }
    @Override
    public ObservableList<?> getDependencies() {
        return FXCollections.singletonObservableList(moo);
    }
    @Override
    public void dispose() {
        super.unbind(moo);
    }
};


See Also:
Binding
NumberBinding
DoubleExpression
Since:
JavaFX 2.0/**
 * Base class that provides most of the functionality needed to implement a
 * {@link Binding} of a {@code double} value.
 * <p>
 * {@code DoubleBinding} 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 DoubleBinding} 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>
 * Below is a simple example of a {@code DoubleBinding} calculating the square-
 * root of a {@link javafx.beans.value.ObservableNumberValue} {@code moo}.
 *
 * <pre>
 * <code>
 * final ObservableDoubleValue moo = ...;
 *
 * DoubleBinding foo = new DoubleBinding() {
 *
 *     {
 *         super.bind(moo);
 *     }
 *
 *     &#x40;Override
 *     protected double computeValue() {
 *         return Math.sqrt(moo.getValue());
 *     }
 * };
 * </code>
 * </pre>
 *
 * Following is the same example with implementations for the optional methods
 * {@link Binding#getDependencies()} and {@link Binding#dispose()}.
 *
 * <pre>
 * <code>
 * final ObservableDoubleValue moo = ...;
 *
 * DoubleBinding foo = new DoubleBinding() {
 *
 *     {
 *         super.bind(moo);
 *     }
 *
 *     &#x40;Override
 *     protected double computeValue() {
 *         return Math.sqrt(moo.getValue());
 *     }
 *
 *     &#x40;Override
 *     public ObservableList&lt;?&gt; getDependencies() {
 *         return FXCollections.singletonObservableList(moo);
 *     }
 *
 *     &#x40;Override
 *     public void dispose() {
 *         super.unbind(moo);
 *     }
 * };
 * </code>
 * </pre>
 *
 * @see Binding
 * @see NumberBinding
 * @see javafx.beans.binding.DoubleExpression
 *
 *
 * @since JavaFX 2.0
 */
public abstract class DoubleBinding extends DoubleExpression implements
        NumberBinding {

    private double value;
    private boolean valid;
    private BindingHelperObserver observer;
    private ExpressionHelper<Number> 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 Number> listener) {
        helper = ExpressionHelper.addListener(helper, this, listener);
    }

    @Override
    public void removeListener(ChangeListener<? super Number> 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.
Params:
dependencies – 
           the dependencies to observe/**
     * 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.
Params:
dependencies – 
           the dependencies to stop observing/**
     * 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 dispose() that is empty. /**
     * A default implementation of {@code dispose()} that is empty.
     */
    @Override
    public void dispose() {
    }

    
A default implementation of getDependencies() that returns an empty ObservableList. 
Returns:
an empty ObservableList/**
     * 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 computeValue(). The method 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 get(). 
Returns:
the current value/**
     * 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 double 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.
/**
     * 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.
 Classes extending DoubleBinding have to provide an implementation of computeValue. 
Returns:
the current value/**
     * Calculates the current value of this binding.
     * <p>
     * Classes extending {@code DoubleBinding} have to provide an implementation
     * of {@code computeValue}.
     *
     * @return the current value
     */
    protected abstract double computeValue();

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