| /* gnu.java.util.DoubleEnumeration |
| Copyright (C) 1998, 1999, 2001 Free Software Foundation, Inc. |
| |
| This file is part of GNU Classpath. |
| |
| GNU Classpath is free software; you can redistribute it and/or modify |
| it under the terms of the GNU General Public License as published by |
| the Free Software Foundation; either version 2, or (at your option) |
| any later version. |
| |
| GNU Classpath is distributed in the hope that it will be useful, but |
| WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| General Public License for more details. |
| |
| You should have received a copy of the GNU General Public License |
| along with GNU Classpath; see the file COPYING. If not, write to the |
| Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA |
| 02110-1301 USA. |
| |
| Linking this library statically or dynamically with other modules is |
| making a combined work based on this library. Thus, the terms and |
| conditions of the GNU General Public License cover the whole |
| combination. |
| |
| As a special exception, the copyright holders of this library give you |
| permission to link this library with independent modules to produce an |
| executable, regardless of the license terms of these independent |
| modules, and to copy and distribute the resulting executable under |
| terms of your choice, provided that you also meet, for each linked |
| independent module, the terms and conditions of the license of that |
| module. An independent module is a module which is not derived from |
| or based on this library. If you modify this library, you may extend |
| this exception to your version of the library, but you are not |
| obligated to do so. If you do not wish to do so, delete this |
| exception statement from your version. */ |
| |
| package gnu.java.util; |
| |
| import java.util.Enumeration; |
| import java.util.NoSuchElementException; |
| |
| |
| /** |
| * This is a helper class that combines two Enumerations. |
| * It returns the elements of the first Enumeration until it has |
| * no more elements and then returns the elements of the second |
| * Enumeration.<br> |
| * |
| * In the default case: |
| * <pre> |
| * doubleEnum = new DoubleEnumeration(enum1, enum2); |
| * while (doubleEnum.hasMoreElements()) { |
| * Object o = doubleEnum.nextElement(); |
| * do_something(o); |
| * } |
| * </pre> |
| * it calls hasMoreElements of the Enumerations as few times as |
| * possible. |
| * The references to the Enumerations are cleared as soon as they have no |
| * more elements to help garbage collecting. |
| * |
| * @author Jochen Hoenicke |
| * @author Mark Wielaard (mark@klomp.org) |
| */ |
| public class DoubleEnumeration implements Enumeration |
| { |
| /** |
| * This is true as long as one of the enumerations has more |
| * elements. |
| * Only valid when hasChecked is true. |
| * Set in <code>hasMoreElements()</code> |
| */ |
| private boolean hasMore; |
| /** |
| * This is true, if it is sure that hasMore indicates wether there are |
| * more elements. |
| * Set to true in <code>hasMoreElements()</code>. |
| * Set to false in <code>getNextElement()</code>. |
| */ |
| private boolean hasChecked; |
| /** |
| * The first enumeration. |
| */ |
| private Enumeration e1; |
| /** |
| * The second enumeration. |
| */ |
| private Enumeration e2; |
| |
| /** |
| * Creates a new Enumeration combining the given two enumerations. |
| * The enumerations mustn't be accessed by other classes. |
| */ |
| public DoubleEnumeration(Enumeration e1, Enumeration e2) |
| { |
| this.e1 = e1; |
| this.e2 = e2; |
| hasChecked = false; |
| } |
| |
| /** |
| * Returns true, if at least one of the two enumerations has more |
| * elements. |
| */ |
| public boolean hasMoreElements() |
| { |
| if (hasChecked) |
| return hasMore; |
| |
| hasMore = (e1 != null && e1.hasMoreElements()); |
| |
| if (!hasMore) { |
| e1 = e2; |
| e2 = null; |
| hasMore = (e1 != null && e1.hasMoreElements()); |
| } |
| |
| hasChecked = true; |
| return hasMore; |
| } |
| |
| /** |
| * Returns the next element. This returns the next element of the |
| * first enumeration, if it has more elements, otherwise the next |
| * element of the second enumeration. If both enumeration don't have |
| * any elements it throws a <code>NoSuchElementException</code>. |
| */ |
| public Object nextElement() |
| { |
| if (!hasMoreElements()) |
| throw new NoSuchElementException(); |
| else { |
| hasChecked = false; |
| return e1.nextElement(); |
| } |
| } |
| } |