Graph Interface: Labeling

There are several operations in the Graph interface about labeling.

Here are four overloaded label methods:

/**
 * Label vertex with an object.
 *
 * @param v Vertex position to label.
 * @param l Label object.
 * @throws PositionException If vertex position is invalid.
 */
void label(Vertex<V> v, Object l) throws PositionException;

/**
 * Label edge with an object.
 *
 * @param e Edge position to label.
 * @param l Label object.
 * @throws PositionException If edge position is invalid.
 */
void label(Edge<E> e, Object l) throws PositionException;

/**
 * Vertex label.
 *
 * @param v Vertex position to query.
 * @return Label object (or null if none).
 * @throws PositionException If vertex position is invalid.
 */
Object label(Vertex<V> v) throws PositionException;

/**
 * Edge label.
 *
 * @param e Edge position to query.
 * @return Label object (or null if none).
 * @throws PositionException If edge position is invalid.
 */
Object label(Edge<E> e) throws PositionException;

And here is a method that clears all the labels:

/**
 * Clear all labels.
 * All labels are null after this.
 */
void clearLabels();

Notice the label type is Object. This means there is no requirement for all labels to have the same data type. Moreover, there is no exception thrown when the label value is null.