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 
18 package 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  */
35 public interface Iterator<E> {
36     /**
37      * Returns true if there is at least one more element, false otherwise.
38      * @see #next
39      */
hasNext()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      */
next()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      */
remove()63     public void remove();
64 }
65