1 /*
2 * $Source$
3 * $Revision$
4 *
5 * Copyright (C) 2000 William Chesters
6 *
7 * Part of Melati (http://melati.org), a framework for the rapid
8 * development of clean, maintainable web applications.
9 *
10 * Melati is free software; Permission is granted to copy, distribute
11 * and/or modify this software under the terms either:
12 *
13 * a) the GNU General Public License as published by the Free Software
14 * Foundation; either version 2 of the License, or (at your option)
15 * any later version,
16 *
17 * or
18 *
19 * b) any version of the Melati Software License, as published
20 * at http://melati.org
21 *
22 * You should have received a copy of the GNU General Public License and
23 * the Melati Software License along with this program;
24 * if not, write to the Free Software Foundation, Inc.,
25 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA to obtain the
26 * GNU General Public License and visit http://melati.org to obtain the
27 * Melati Software License.
28 *
29 * Feel free to contact the Developers of Melati (http://melati.org),
30 * if you would like to work out a different arrangement than the options
31 * outlined here. It is our intention to allow Melati to be used by as
32 * wide an audience as possible.
33 *
34 * This program is distributed in the hope that it will be useful,
35 * but WITHOUT ANY WARRANTY; without even the implied warranty of
36 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
37 * GNU General Public License for more details.
38 *
39 * Contact details for copyright holder:
40 *
41 * William Chesters <williamc At paneris.org>
42 * http://paneris.org/~williamc
43 * Obrechtstraat 114, 2517VX Den Haag, The Netherlands
44 */
45
46 package org.melati.poem.util;
47
48 import java.util.Enumeration;
49 import java.util.NoSuchElementException;
50
51 /**
52 * An <code>Enumeration</code> created by flattening
53 * an <code>Enumeration</code> of <code>Enumeration</code>s
54 * or flattening two <code>Enumeration</code>s .
55 */
56 public class FlattenedEnumeration<T> implements Enumeration<T> {
57 private Enumeration<Enumeration<T>> enumerations;
58 private Enumeration<T> enumeration = null;
59
60 /**
61 * Constructor.
62 * @param enumerations an Enumeration of Enumerations
63 */
64 public FlattenedEnumeration(Enumeration<Enumeration<T>> enumerations) {
65 this.enumerations = enumerations;
66 }
67
68 /**
69 * Constructor given two Enumerations to flatten into one.
70 * @param a head Enumeration
71 * @param b tail Enumeration
72 */
73 public FlattenedEnumeration(Enumeration<T> a, Enumeration<T> b) {
74 this.enumerations =
75 new ConsEnumeration<Enumeration<T>>(a, new ConsEnumeration<Enumeration<T>>(b, new EmptyEnumeration<Enumeration<T>>()));
76 }
77
78 private void probe() {
79 while ((enumeration == null || !enumeration.hasMoreElements()) &&
80 enumerations.hasMoreElements())
81 enumeration = (Enumeration<T>)enumerations.nextElement();
82 }
83
84 /**
85 * {@inheritDoc}
86 * @see java.util.Enumeration#hasMoreElements()
87 */
88 public synchronized boolean hasMoreElements() {
89 probe();
90 return enumeration != null && enumeration.hasMoreElements();
91 }
92
93 /**
94 * {@inheritDoc}
95 * @see java.util.Enumeration#nextElement()
96 */
97 public synchronized T nextElement() {
98 probe();
99 if (enumeration == null)
100 throw new NoSuchElementException();
101 return enumeration.nextElement();
102 }
103 }