* IllegalArgumentException}.
   */
  boolean allowsSelfLoops();

  /** Returns the order of iteration for the elements of {@link #nodes()}. */
  ElementOrder<N> nodeOrder();

  /** Returns the order of iteration for the elements of {@link #edges()}. */
  ElementOrder<E> edgeOrder();

  //
  // Element-level accessors
  //

  /**

    return new Strings();
  }

  @Override
  public Collection<String> create(Object... elements) {
    String[] array = new String[elements.length];
    int i = 0;
    for (Object e : elements) {
      array[i++] = (String) e;
    }
    return create(array);
  }

  protected abstract Collection<String> create(String[] elements);

  @Override
  public String[] createArray(int length) {
    return new String[length];

    return new Strings();
  }

  @Override
  public Queue<String> create(Object... elements) {
    String[] array = new String[elements.length];
    int i = 0;
    for (Object e : elements) {
      array[i++] = (String) e;
    }
    return create(array);
  }

  protected abstract Queue<String> create(String[] elements);

  @Override
  public String[] createArray(int length) {
    return new String[length];

    this.equivalence = checkNotNull(equivalence);
  }

  /**
   * Different orderings for combining the elements of an input array, which must all produce the
   * same result.
   */
  enum CollectStrategy {
    /** Get one accumulator and accumulate the elements into it sequentially. */
    SEQUENTIAL {
      @Override

      long tmp = array[i];
      array[i] = array[j];
      array[j] = tmp;
    }
  }

  /**
   * Performs a right rotation of {@code array} of "distance" places, so that the first element is
   * moved to index "distance", and the element at index {@code i} ends up at index {@code (distance
   * + i) mod array.length}. This is equivalent to {@code Collections.rotate(Longs.asList(array),

    @Override
    protected List<Short> create(Short[] elements) {
      return asList(elements);
    }
  }

  public static final class ShortsAsListHeadSubListGenerator extends TestShortListGenerator {
    @Override
    protected List<Short> create(Short[] elements) {
      Short[] suffix = {Short.MIN_VALUE, Short.MAX_VALUE};
      Short[] all = concat(elements, suffix);
      return asList(all).subList(0, elements.length);

    protected List<Long> create(Long[] elements) {
      return asList(elements);
    }
  }

  public static final class LongsAsListHeadSubListGenerator extends TestLongListGenerator {
    @Override
    protected List<Long> create(Long[] elements) {
      Long[] suffix = {Long.MIN_VALUE, Long.MAX_VALUE};
      Long[] all = concat(elements, suffix);
      return asList(all).subList(0, elements.length);
    }
  }

    @Override
    protected List<Short> create(Short[] elements) {
      return asList(elements);
    }
  }

  public static final class ShortsAsListHeadSubListGenerator extends TestShortListGenerator {
    @Override
    protected List<Short> create(Short[] elements) {
      Short[] suffix = {Short.MIN_VALUE, Short.MAX_VALUE};
      Short[] all = concat(elements, suffix);
      return asList(all).subList(0, elements.length);

    public static final String CONTAINS = "contains:";

    /** XML element name for collections container. */
    protected static final String COLLECTIONS = "collections";

    /** XML element name for individual collection. */
    protected static final String COLLECTION = "collection";

    /** XML element name for global parameters container. */
    protected static final String GLOBALPARAMS = "globalparams";

  /** Test an empty collection. */
  ZERO(0),
  /** Test a one-element collection. */
  ONE(1),
  /** Test a three-element collection. */
  SEVERAL(3),
  /*
   * TODO: add VERY_LARGE, noting that we currently assume that the fourth
   * sample element is not in any collection
   */

  ANY(ZERO, ONE, SEVERAL);

  private final Set<Feature<? super Collection>> implied;