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3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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8    * particular file as subject to the "Classpath" exception as provided
9    * by Oracle in the LICENSE file that accompanied this code.
10   *
11   * This code is distributed in the hope that it will be useful, but WITHOUT
12   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14   * version 2 for more details (a copy is included in the LICENSE file that
15   * accompanied this code).
16   *
17   * You should have received a copy of the GNU General Public License version
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19   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20   *
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24   */
25  
26  package java.util;
27  
28  import java.util.function.Consumer;
29  
30  /**
31   * An iterator over a collection.  {@code Iterator} takes the place of
32   * {@link Enumeration} in the Java Collections Framework.  Iterators
33   * differ from enumerations in two ways:
34   *
35   * <ul>
36   *      <li> Iterators allow the caller to remove elements from the
37   *           underlying collection during the iteration with well-defined
38   *           semantics.
39   *      <li> Method names have been improved.
40   * </ul>
41   *
42   * <p>This interface is a member of the
43   * <a href="{@docRoot}/../technotes/guides/collections/index.html">
44   * Java Collections Framework</a>.
45   *
46   * @param <E> the type of elements returned by this iterator
47   *
48   * @author  Josh Bloch
49   * @see Collection
50   * @see ListIterator
51   * @see Iterable
52   * @since 1.2
53   */
54  public interface Iterator<E> {
55      /**
56       * Returns {@code true} if the iteration has more elements.
57       * (In other words, returns {@code true} if {@link #next} would
58       * return an element rather than throwing an exception.)
59       *
60       * @return {@code true} if the iteration has more elements
61       */
62      boolean hasNext();
63  
64      /**
65       * Returns the next element in the iteration.
66       *
67       * @return the next element in the iteration
68       * @throws NoSuchElementException if the iteration has no more elements
69       */
70      E next();
71  
72      /**
73       * Removes from the underlying collection the last element returned
74       * by this iterator (optional operation).  This method can be called
75       * only once per call to {@link #next}.  The behavior of an iterator
76       * is unspecified if the underlying collection is modified while the
77       * iteration is in progress in any way other than by calling this
78       * method.
79       *
80       * @implSpec
81       * The default implementation throws an instance of
82       * {@link UnsupportedOperationException} and performs no other action.
83       *
84       * @throws UnsupportedOperationException if the {@code remove}
85       *         operation is not supported by this iterator
86       *
87       * @throws IllegalStateException if the {@code next} method has not
88       *         yet been called, or the {@code remove} method has already
89       *         been called after the last call to the {@code next}
90       *         method
91       */
92      default void remove() {
93          throw new UnsupportedOperationException("remove");
94      }
95  
96      /**
97       * Performs the given action for each remaining element until all elements
98       * have been processed or the action throws an exception.  Actions are
99       * performed in the order of iteration, if that order is specified.
100      * Exceptions thrown by the action are relayed to the caller.
101      *
102      * @implSpec
103      * <p>The default implementation behaves as if:
104      * <pre>{@code
105      *     while (hasNext())
106      *         action.accept(next());
107      * }</pre>
108      *
109      * @param action The action to be performed for each element
110      * @throws NullPointerException if the specified action is null
111      * @since 1.8
112      */
113     default void forEachRemaining(Consumer<? super E> action) {
114         Objects.requireNonNull(action);
115         while (hasNext())
116             action.accept(next());
117     }
118 }