1 /*

     2  * Copyright 1997-2006 Sun Microsystems, Inc.  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.  Sun designates this

     8  * particular file as subject to the "Classpath" exception as provided

     9  * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

    22  * CA 95054 USA or visit www.sun.com if you need additional information or

    23  * have any questions.

    24  */

    25 

    26 package java.util;

    27 

    28 /**

    29  * An iterator over a collection.  {@code Iterator} takes the place of

    30  * {@link Enumeration} in the Java Collections Framework.  Iterators

    31  * differ from enumerations in two ways:

    32  *

    33  * <ul>

    34  *      <li> Iterators allow the caller to remove elements from the

    35  *           underlying collection during the iteration with well-defined

    36  *           semantics.

    37  *      <li> Method names have been improved.

    38  * </ul>

    39  *

    40  * <p>This interface is a member of the

    41  * <a href="{@docRoot}/../technotes/guides/collections/index.html">

    42  * Java Collections Framework</a>.

    43  *

    44  * @author  Josh Bloch

    45  * @see Collection

    46  * @see ListIterator

    47  * @see Iterable

    48  * @since 1.2

    49  */

    50 public interface Iterator<E> {

    51     /**

    52      * Returns {@code true} if the iteration has more elements.

    53      * (In other words, returns {@code true} if {@link #next} would

    54      * return an element rather than throwing an exception.)

    55      *

    56      * @return {@code true} if the iteration has more elements

    57      */

    58     boolean hasNext();

    59 

    60     /**

    61      * Returns the next element in the iteration.

    62      *

    63      * @return the next element in the iteration

    64      * @throws NoSuchElementException if the iteration has no more elements

    65      */

    66     E next();

    67 

    68     /**

    69      * Removes from the underlying collection the last element returned

    70      * by this iterator (optional operation).  This method can be called

    71      * only once per call to {@link #next}.  The behavior of an iterator

    72      * is unspecified if the underlying collection is modified while the

    73      * iteration is in progress in any way other than by calling this

    74      * method.

    75      *

    76      * @throws UnsupportedOperationException if the {@code remove}

    77      *         operation is not supported by this iterator

    78      *

    79      * @throws IllegalStateException if the {@code next} method has not

    80      *         yet been called, or the {@code remove} method has already

    81      *         been called after the last call to the {@code next}

    82      *         method

    83      */

    84     void remove();

    85 }