case NEW:
            snapshot = new StateSnapshot(TERMINATED);
            enqueueTerminatedEvent(NEW);
            break;
          case STARTING:
            snapshot = new StateSnapshot(STARTING, true, null);
            enqueueStoppingEvent(STARTING);
            doCancelStart();
            break;
          case RUNNING:
            snapshot = new StateSnapshot(STOPPING);

   * exceptions.
   *
   * **The caller must [close][Snapshot.close]** each snapshot returned by [Iterator.next]. Failing
   * to do so leaks open files!
   */
  @Synchronized
  @Throws(IOException::class)
  fun snapshots(): MutableIterator<Snapshot> {
    initialize()
    return object : MutableIterator<Snapshot> {
      /** Iterate a copy of the entries to defend against concurrent modification errors. */

          case NEW:
            snapshot = new StateSnapshot(TERMINATED);
            enqueueTerminatedEvent(NEW);
            break;
          case STARTING:
            snapshot = new StateSnapshot(STARTING, true, null);
            enqueueStoppingEvent(STARTING);
            doCancelStart();
            break;
          case RUNNING:
            snapshot = new StateSnapshot(STOPPING);

    val key = key(request.url)
    val snapshot: DiskLruCache.Snapshot =
      try {
        cache[key] ?: return null
      } catch (_: IOException) {
        return null // Give up because the cache cannot be read.
      }

    val entry: Entry =
      try {
        Entry(snapshot.getSource(ENTRY_METADATA))
      } catch (_: IOException) {
        snapshot.closeQuietly()
        return null
      }

    accumulator.addAll(values);
    return accumulator.snapshot();
  }

  /**
   * Returns statistics over a dataset containing the given values.
   *
   * @param values a series of values
   */
  public static Stats of(double... values) {
    StatsAccumulator accumulator = new StatsAccumulator();
    accumulator.addAll(values);
    return accumulator.snapshot();
  }

  /**

  }

  /** Returns an immutable snapshot of the current statistics. */
  public PairedStats snapshot() {
    return new PairedStats(xStats.snapshot(), yStats.snapshot(), sumOfProductsOfDeltas);
  }

  /** Returns the number of pairs in the dataset. */
  public long count() {
    return xStats.count();
  }

  /** Returns an immutable snapshot of the statistics on the {@code x} values alone. */

    }

    /**
     * Gets the actual version string for a SNAPSHOT artifact by parsing the snapshot metadata.
     *
     * @param builder the document builder to use for parsing XML
     * @param pluginUrl the URL of the plugin
     * @param version the snapshot version
     * @return the actual version string with timestamp and build number, or null if not found

    }

    public void test_getSnapshotActualVersion_valid() {
        String snapshotXml = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n" + "<metadata>\n" + "  <snapshot>\n"
                + "    <timestamp>20180814.210714</timestamp>\n" + "    <buildNumber>10</buildNumber>\n" + "  </snapshot>\n"
                + "</metadata>";

        PluginHelper testHelper = new PluginHelper() {
            @Override

    oneValueAccumulator = new PairedStatsAccumulator();
    oneValueAccumulator.add(ONE_VALUE, OTHER_ONE_VALUE);

    oneValueAccumulatorByAddAllEmptyPairedStats = new PairedStatsAccumulator();
    oneValueAccumulatorByAddAllEmptyPairedStats.add(ONE_VALUE, OTHER_ONE_VALUE);
    oneValueAccumulatorByAddAllEmptyPairedStats.addAll(emptyAccumulator.snapshot());

 *
 * @author Pete Gillin
 * @since 20.0
 */
@J2ktIncompatible
@GwtIncompatible
public final class PairedStats implements Serializable {

  private final Stats xStats;
  private final Stats yStats;
  private final double sumOfProductsOfDeltas;

  /**
   * Internal constructor. Users should use {@link PairedStatsAccumulator#snapshot}.
   *