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 }