1 /*

     2  * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.  Oracle designates this

     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

    18  * 2 along with this work; if not, write to the Free Software Foundation,

    19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    20  *

    21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    22  * or visit www.oracle.com if you need additional information or have any

    23  * questions.

    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 }