/**
  * Returns a clone of this dataset.
  *
  * @return A clone.
  * @throws CloneNotSupportedException if cloning is not possible.
  */
 public Object clone() throws CloneNotSupportedException {
   DefaultBoxAndWhiskerCategoryDataset clone = (DefaultBoxAndWhiskerCategoryDataset) super.clone();
   clone.data = (KeyedObjects2D) this.data.clone();
   return clone;
 }