1/*
2 *  Licensed to the Apache Software Foundation (ASF) under one or more
3 *  contributor license agreements.  See the NOTICE file distributed with
4 *  this work for additional information regarding copyright ownership.
5 *  The ASF licenses this file to You under the Apache License, Version 2.0
6 *  (the "License"); you may not use this file except in compliance with
7 *  the License.  You may obtain a copy of the License at
8 *
9 *     http://www.apache.org/licenses/LICENSE-2.0
10 *
11 *  Unless required by applicable law or agreed to in writing, software
12 *  distributed under the License is distributed on an "AS IS" BASIS,
13 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 *  See the License for the specific language governing permissions and
15 *  limitations under the License.
16 */
17
18package java.util;
19
20/**
21 * An iterator over a sequence of objects, such as a collection.
22 *
23 * <p>If a collection has been changed since the iterator was created,
24 * methods {@code next} and {@code hasNext()} may throw a {@code ConcurrentModificationException}.
25 * It is not possible to guarantee that this mechanism works in all cases of unsynchronized
26 * concurrent modification. It should only be used for debugging purposes. Iterators with this
27 * behavior are called fail-fast iterators.
28 *
29 * <p>Implementing {@link Iterable} and returning an {@code Iterator} allows your
30 * class to be used as a collection with the enhanced for loop.
31 *
32 * @param <E>
33 *            the type of object returned by the iterator.
34 */
35public interface Iterator<E> {
36    /**
37     * Returns true if there is at least one more element, false otherwise.
38     * @see #next
39     */
40    public boolean hasNext();
41
42    /**
43     * Returns the next object and advances the iterator.
44     *
45     * @return the next object.
46     * @throws NoSuchElementException
47     *             if there are no more elements.
48     * @see #hasNext
49     */
50    public E next();
51
52    /**
53     * Removes the last object returned by {@code next} from the collection.
54     * This method can only be called once between each call to {@code next}.
55     *
56     * @throws UnsupportedOperationException
57     *             if removing is not supported by the collection being
58     *             iterated.
59     * @throws IllegalStateException
60     *             if {@code next} has not been called, or {@code remove} has
61     *             already been called after the last call to {@code next}.
62     */
63    public void remove();
64}
65