How to use

getKey

method

in

org.jfree.data.xy.VectorSeries

/**
 * Returns the key for a series.
 *
 * @param series  the series index (in the range {@code 0} to
 *     {@code getSeriesCount() - 1}).
 *
 * @return The key for a series.
 *
 * @throws IllegalArgumentException if {@code series} is not in the
 *     specified range.
 */
@Override
public Comparable getSeriesKey(int series) {
  // defer argument checking
  return getSeries(series).getKey();
}

/**
 * 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.
 */
public Comparable getSeriesKey(int series) {
  // defer argument checking
  return getSeries(series).getKey();
}