*     ...
 * }
 * </pre>
 *
 * @author koichik
 * @param <E> the element type
 */
public class MultiIterator<E> implements Iterator<E> {

    /** Array of {@link Iterator}s. */
    protected final Iterator<E>[] iterators;

    /** Index of the currently iterated {@link Iterator}. */
    protected int index;

    /**
     * Returns an {@link Iterable} that wraps a {@link MultiIterator} for use in a for-each statement.

import static org.codelibs.core.misc.AssertionUtil.assertArgumentNotNull;

import java.util.Iterator;
import java.util.NoSuchElementException;

import org.codelibs.core.exception.ClUnsupportedOperationException;
import org.codelibs.core.message.MessageFormatter;

/**
 * An {@link Iterator} that iterates through the inheritance hierarchy of a class towards its superclasses.
 * <p>
 * Usage example:
 * </p>
 *

        @Override
        @Nullable N visitNext(Deque<Iterator<? extends N>> horizon) {
          Iterator<? extends N> top = horizon.getFirst();
          if (top.hasNext()) {
            return checkNotNull(top.next());
          }
          horizon.removeFirst();
          return null;
        }
      };
    }

    final Iterator<N> breadthFirst(Iterator<? extends N> startNodes) {

        return set1.isEmpty() && set2.isEmpty();
      }

      @Override
      public UnmodifiableIterator<E> iterator() {
        return new AbstractIterator<E>() {
          final Iterator<? extends E> itr1 = set1.iterator();
          final Iterator<? extends E> itr2 = set2.iterator();

          @Override
          protected @Nullable E computeNext() {
            if (itr1.hasNext()) {

        : newArrayList(elements.iterator());
  }

  /**
   * Creates a <i>mutable</i> {@code ArrayList} instance containing the given elements; a very thin
   * shortcut for creating an empty list and then calling {@link Iterators#addAll}.
   *
   * <p><b>Note:</b> if mutability is not required and the elements are non-null, use {@link
   * ImmutableList#copyOf(Iterator)} instead.
   */

        : newArrayList(elements.iterator());
  }

  /**
   * Creates a <i>mutable</i> {@code ArrayList} instance containing the given elements; a very thin
   * shortcut for creating an empty list and then calling {@link Iterators#addAll}.
   *
   * <p><b>Note:</b> if mutability is not required and the elements are non-null, use {@link
   * ImmutableList#copyOf(Iterator)} instead.
   */

        return set1.isEmpty() && set2.isEmpty();
      }

      @Override
      public UnmodifiableIterator<E> iterator() {
        return new AbstractIterator<E>() {
          final Iterator<? extends E> itr1 = set1.iterator();
          final Iterator<? extends E> itr2 = set2.iterator();

          @Override
          protected @Nullable E computeNext() {
            if (itr1.hasNext()) {

   * For example, two graphs may be considered equal even if one allows self-loops and the other
   * doesn't. Additionally, the order in which nodes or edges are added to the graph, and the order
   * in which they are iterated over, are irrelevant.
   *
   * <p>A reference implementation of this is provided by {@link AbstractValueGraph#equals(Object)}.
   */
  @Override
  boolean equals(@Nullable Object object);

  /**

   * For example, two graphs may be considered equal even if one allows self-loops and the other
   * doesn't. Additionally, the order in which nodes or edges are added to the graph, and the order
   * in which they are iterated over, are irrelevant.
   *
   * <p>A reference implementation of this is provided by {@link AbstractGraph#equals(Object)}.
   */
  @Override
  boolean equals(@Nullable Object object);

  /**

   * close the open underlying stream.
   *
   * <p>Note: The input {@code Iterator} will be copied to an {@code ImmutableList} when this method
   * is called. This will fail if the iterator is infinite and may cause problems if the iterator
   * eagerly fetches data for each source when iterated (rather than producing sources that only