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   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
   * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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   */
  
  package java.util;
  
  import java.util.function.Consumer;
  
  /**
   * An iterator over a collection.  {@code Iterator} takes the place of
   * {@link Enumeration} in the Java Collections Framework.  Iterators
   * differ from enumerations in two ways:
   *
   * <ul>
   *      <li> Iterators allow the caller to remove elements from the
   *           underlying collection during the iteration with well-defined
   *           semantics.
   *      <li> Method names have been improved.
   * </ul>
   *
   * <p>This interface is a member of the
   * <a href="{@docRoot}/../technotes/guides/collections/index.html">
   * Java Collections Framework</a>.
   *
   * @param <E> the type of elements returned by this iterator
   *
   * @author  Josh Bloch
   * @see Collection
   * @see ListIterator
   * @see Iterable
   * @since 1.2
   */
  public interface Iterator<E> {
      /**
       * Returns {@code true} if the iteration has more elements.
       * (In other words, returns {@code true} if {@link #next} would
       * return an element rather than throwing an exception.)
       *
       * @return {@code true} if the iteration has more elements
       */
      boolean hasNext();
  
      /**
       * Returns the next element in the iteration.
       *
       * @return the next element in the iteration
       * @throws NoSuchElementException if the iteration has no more elements
       */
      E next();
  
      /**
       * Removes from the underlying collection the last element returned
       * by this iterator (optional operation).  This method can be called
       * only once per call to {@link #next}.  The behavior of an iterator
       * is unspecified if the underlying collection is modified while the
       * iteration is in progress in any way other than by calling this
       * method.
       *
       * @implSpec
       * The default implementation throws an instance of
       * {@link UnsupportedOperationException} and performs no other action.
       *
       * @throws UnsupportedOperationException if the {@code remove}
       *         operation is not supported by this iterator
       *
       * @throws IllegalStateException if the {@code next} method has not
       *         yet been called, or the {@code remove} method has already
       *         been called after the last call to the {@code next}
       *         method
       */
      default void remove() {
          throw new UnsupportedOperationException("remove");
      }
  
      /**
       * Performs the given action for each remaining element until all elements
       * have been processed or the action throws an exception.  Actions are
       * performed in the order of iteration, if that order is specified.
       * Exceptions thrown by the action are relayed to the caller.
       *
       * @implSpec
       * <p>The default implementation behaves as if:
       * <pre>{@code
       *     while (hasNext())
       *         action.accept(next());
       * }</pre>
       *
       * @param action The action to be performed for each element
       * @throws NullPointerException if the specified action is null
       * @since 1.8
       */
      default void forEachRemaining(Consumer<? super E> action) {
          Objects.requireNonNull(action);
          while (hasNext())
              action.accept(next());
      }
  }
  