Iterator.java revision adc854b798c1cfe3bfd4c27d68d5cee38ca617da 
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/**
22 * An Iterator is used to sequence over a collection of objects. Conceptual, an
23 * iterator is always positioned between two elements of a collection. A fresh
24 * iterator is always positioned in front of the first element.
25 *
26 * If a collection has been changed since its creation, methods {@code next} and
27 * {@code hasNext()} may throw a {@code ConcurrentModificationException}.
28 * Iterators with this behavior are called fail-fast iterators.
29 *
30 * @since Android 1.0
31 */
32public interface Iterator<E> {
33    /**
34     * Returns whether there are more elements to iterate, i.e. whether the
35     * iterator is positioned in front of an element.
36     *
37     * @return {@code true} if there are more elements, {@code false} otherwise.
38     * @see #next
39     * @since Android 1.0
40     */
41    public boolean hasNext();
42
43    /**
44     * Returns the next object in the iteration, i.e. returns the element in
45     * front of the iterator and advances the iterator by one position.
46     *
47     * @return the next object.
48     * @throws NoSuchElementException
49     *             if there are no more elements.
50     * @see #hasNext
51     * @since Android 1.0
52     */
53    public E next();
54
55    /**
56     * Removes the last object returned by {@code next} from the collection.
57     * This method can only be called once after {@code next} was called.
58     *
59     * @throws UnsupportedOperationException
60     *             if removing is not supported by the collection being
61     *             iterated.
62     * @throws IllegalStateException
63     *             if {@code next} has not been called, or {@code remove} has
64     *             already been called after the last call to {@code next}.
65     * @since Android 1.0
66     */
67    public void remove();
68}
69