try {
      builder.buildOrThrow();
      fail("Expected exception from duplicate keys");
    } catch (IllegalArgumentException expected) {
      // We don't really care which values the exception message contains, but they should be
      // different from each other. If buildKeepingLast() collapsed duplicates, that might end up
      // not being true.

    return (1 << (metadata & CompactHashing.HASH_TABLE_BITS_MASK)) - 1;
  }

  void incrementModCount() {
    metadata += CompactHashing.MODIFICATION_COUNT_INCREMENT;
  }

  /**
   * Mark an access of the specified entry. Used only in {@code CompactLinkedHashMap} for LRU
   * ordering.
   */
  void accessEntry(int index) {
    // no-op by default
  }

  @CanIgnoreReturnValue
  @Override

   * this still yields higher concurrency than full synchronization.
   *
   * <p>Defaults to 4. <b>Note:</b>The default may change in the future. If you care about this
   * value, you should always choose it explicitly.
   *
   * <p>The current implementation uses the concurrency level to create a fixed number of hashtable

    return s.charAt(rand.nextInt(s.length()));
  }

  /**
   * Provides samples on a random distribution derived from the web.
   *
   * <p>Adapted from data provided by Mark Davis.
   *
   * @author Christopher Swenson
   */
  static class CharSamples {

    static {
      populateProb1();
      populateProb2();
      populateChars1();
      populateChars2();

      Class<?> cls;
      try {
        cls = classInfo.load();
      } catch (NoClassDefFoundError e) {
        // In case there were linking problems, this is probably not a class we care to test anyway.
        logger.log(Level.SEVERE, "Cannot load class " + classInfo + ", skipping...", e);
        continue;
      }
      if (!cls.isInterface()) {
        classes.add(cls);
      }
    }

   * exercise null handling fail on those subcollections.
   */
  public abstract static class NullsBefore implements Comparator<@Nullable String>, Serializable {
    /*
     * We don't serialize this class in GWT, so we don't care about whether GWT will serialize this
     * field.
     */
    @GwtTransient private final String justAfterNull;

    protected NullsBefore(String justAfterNull) {
      if (justAfterNull == null) {

  /**
   * Determines whether an edge has already been used during traversal. In the directed case a cycle
   * is always detected before reusing an edge, so no special logic is required. In the undirected
   * case, we must take care not to "backtrack" over an edge (i.e. going from A to B and then going
   * from B to A).
   */
  private static boolean canTraverseWithoutReusingEdge(