gt:         VectorSeriesCollection that = (VectorSeriesCollection) obj;
context: /* ===========================================================
   * JFreeChart : a free chart library for the Java(tm) platform
   * ===========================================================
   *
   * (C) Copyright 2000-2014, by Object Refinery Limited and Contributors.
   *
   * Project Info:  http://www.jfree.org/jfreechart/index.html
   *
   * This library is free software; you can redistribute it and/or modify it
   * under the terms of the GNU Lesser General Public License as published by
   * the Free Software Foundation; either version 2.1 of the License, or
   * (at your option) any later version.
   *
   * This library 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 Lesser General Public
   * License for more details.
   *
   * You should have received a copy of the GNU Lesser General Public
   * License along with this library; if not, write to the Free Software
   * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
   * USA.
   *
   * [Oracle and Java are registered trademarks of Oracle and/or its affiliates. 
   * Other names may be trademarks of their respective owners.]
   *
   * ---------------------------
   * VectorSeriesCollection.java
   * ---------------------------
   * (C) Copyright 2007-2014, by Object Refinery Limited.
   *
   * Original Author:  David Gilbert (for Object Refinery Limited);
   * Contributor(s):   -;
   *
   * Changes
   * -------
   * 30-Jan-2007 : Version 1 (DG);
   * 24-May-2007 : Added indexOf(), removeSeries() and removeAllSeries()
   *               methods (DG);
   * 25-May-2007 : Moved from experimental to the main source tree (DG);
   * 22-Apr-2008 : Implemented PublicCloneable (DG);
   * 16-Jun-2012 : Removed JCommon dependencies (DG);
   *
   */
  
  package org.jfree.data.xy;
  
  import java.io.Serializable;
  import java.util.List;
  import org.jfree.chart.util.ObjectUtils;
  import org.jfree.chart.util.ParamChecks;
  import org.jfree.chart.util.PublicCloneable;
  import org.jfree.data.general.DatasetChangeEvent;
  
  /**
   * A collection of {@link VectorSeries} objects.
   *
   * @since 1.0.6
   */
  public class VectorSeriesCollection extends AbstractXYDataset
          implements VectorXYDataset, PublicCloneable, Serializable {
  
      /** Storage for the data series. */
      private List<VectorSeries> data;
  
      /**
       * Creates a new instance of <code>VectorSeriesCollection</code>.
       */
      public VectorSeriesCollection() {
          this.data = new java.util.ArrayList<VectorSeries>();
      }
  
      /**
       * Adds a series to the collection and sends a {@link DatasetChangeEvent}
       * to all registered listeners.
       *
       * @param series  the series (<code>null</code> not permitted).
       */
      public void addSeries(VectorSeries series) {
          ParamChecks.nullNotPermitted(series, "series");
          this.data.add(series);
          series.addChangeListener(this);
          fireDatasetChanged();
      }
  
      /**
       * Removes the specified series from the collection and sends a
       * {@link DatasetChangeEvent} to all registered listeners.
       *
       * @param series  the series (<code>null</code> not permitted).
       *
       * @return A boolean indicating whether the series has actually been
       *         removed.
       */
      public boolean removeSeries(VectorSeries series) {
          ParamChecks.nullNotPermitted(series, "series");
          boolean removed = this.data.remove(series);
          if (removed) {
              series.removeChangeListener(this);
              fireDatasetChanged();
          }
          return removed;
      }
  
      /**
       * Removes all the series from the collection and sends a
       * {@link DatasetChangeEvent} to all registered listeners.
       */
      public void removeAllSeries() {
          // deregister the collection as a change listener to each series in the
          // collection
          for (VectorSeries series : this.data) {
              series.removeChangeListener(this);
          }
          // remove all the series from the collection and notify listeners.
          this.data.clear();
          fireDatasetChanged();
      }
  
      /**
       * Returns the number of series in the collection.
       *
       * @return The series count.
       */
      @Override
      public int getSeriesCount() {
          return this.data.size();
      }
  
      /**
       * Returns a series from the collection.
       *
       * @param series  the series index (zero-based).
       *
       * @return The series.
       *
       * @throws IllegalArgumentException if <code>series</code> is not in the
       *     range <code>0</code> to <code>getSeriesCount() - 1</code>.
       */
      public VectorSeries getSeries(int series) {
          if ((series < 0) || (series >= getSeriesCount())) {
              throw new IllegalArgumentException("Series index out of bounds");
          }
          return this.data.get(series);
      }
  
      /**
       * Returns the key for a series.
       *
       * @param series  the series index (in the range <code>0</code> to
       *     <code>getSeriesCount() - 1</code>).
       *
       * @return The key for a series.
       *
       * @throws IllegalArgumentException if <code>series</code> is not in the
       *     specified range.
       */
      @Override
      public Comparable getSeriesKey(int series) {
          // defer argument checking
          return getSeries(series).getKey();
      }
  
      /**
       * Returns the index of the specified series, or -1 if that series is not
       * present in the dataset.
       *
       * @param series  the series (<code>null</code> not permitted).
       *
       * @return The series index.
       */
      public int indexOf(VectorSeries series) {
          ParamChecks.nullNotPermitted(series, "series");
          return this.data.indexOf(series);
      }
  
      /**
       * Returns the number of items in the specified series.
       *
       * @param series  the series (zero-based index).
       *
       * @return The item count.
       *
       * @throws IllegalArgumentException if <code>series</code> is not in the
       *     range <code>0</code> to <code>getSeriesCount() - 1</code>.
       */
      @Override
      public int getItemCount(int series) {
          // defer argument checking
          return getSeries(series).getItemCount();
      }
  
      /**
       * Returns the x-value for an item within a series.
       *
       * @param series  the series index.
       * @param item  the item index.
       *
       * @return The x-value.
       */
      @Override
      public double getXValue(int series, int item) {
          VectorSeries s = this.data.get(series);
          VectorDataItem di = (VectorDataItem) s.getDataItem(item);
          return di.getXValue();
      }
  
      /**
       * Returns the x-value for an item within a series.  Note that this method
       * creates a new {@link Double} instance every time it is called---use
       * {@link #getXValue(int, int)} instead, if possible.
       *
       * @param series  the series index.
       * @param item  the item index.
       *
       * @return The x-value.
       */
      @Override
      public Number getX(int series, int item) {
          return getXValue(series, item);
      }
  
      /**
       * Returns the y-value for an item within a series.
       *
       * @param series  the series index.
       * @param item  the item index.
       *
       * @return The y-value.
       */
      @Override
      public double getYValue(int series, int item) {
          VectorSeries s = this.data.get(series);
          VectorDataItem di = (VectorDataItem) s.getDataItem(item);
          return di.getYValue();
      }
  
      /**
       * Returns the y-value for an item within a series.  Note that this method
       * creates a new {@link Double} instance every time it is called---use
       * {@link #getYValue(int, int)} instead, if possible.
       *
       * @param series  the series index.
       * @param item  the item index.
       *
       * @return The y-value.
       */
      @Override
      public Number getY(int series, int item) {
          return getYValue(series, item);
      }
  
      /**
       * Returns the vector for an item in a series.
       *
       * @param series  the series index.
       * @param item  the item index.
       *
       * @return The vector (possibly <code>null</code>).
       */
      @Override
      public Vector getVector(int series, int item) {
          VectorSeries s = this.data.get(series);
          VectorDataItem di = (VectorDataItem) s.getDataItem(item);
          return di.getVector();
      }
  
      /**
       * Returns the x-component of the vector for an item in a series.
       *
       * @param series  the series index.
       * @param item  the item index.
       *
       * @return The x-component of the vector.
       */
      @Override
      public double getVectorXValue(int series, int item) {
          VectorSeries s = this.data.get(series);
          VectorDataItem di = (VectorDataItem) s.getDataItem(item);
          return di.getVectorX();
      }
  
      /**
       * Returns the y-component of the vector for an item in a series.
       *
       * @param series  the series index.
       * @param item  the item index.
       *
       * @return The y-component of the vector.
       */
      @Override
      public double getVectorYValue(int series, int item) {
          VectorSeries s = this.data.get(series);
          VectorDataItem di = (VectorDataItem) s.getDataItem(item);
          return di.getVectorY();
      }
  
      /**
       * Tests this instance for equality with an arbitrary object.
       *
       * @param obj  the object (<code>null</code> permitted).
       *
       * @return A boolean.
       */
      @Override
      public boolean equals(Object obj) {
          if (obj == this) {
              return true;
          }
          if (!(obj instanceof VectorSeriesCollection)) {
              return false;
          }
  