1 //----------------------------------------------------------------------
2 //
3 // PerfectJPattern: "Design patterns are good but components are better!"
4 // NullResult.java Copyright (c) 2009 Giovanni Azua Garcia
5 // bravegag@hotmail.com
6 //
7 // This program is free software; you can redistribute it and/or
8 // modify it under the terms of the GNU General Public License
9 // as published by the Free Software Foundation; either version 3
10 // of the License, or (at your option) any later version.
11 //
12 // This program is distributed in the hope that it will be useful,
13 // but WITHOUT ANY WARRANTY; without even the implied warranty of
14 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 // GNU General Public License for more details.
16 //
17 // You should have received a copy of the GNU General Public License
18 // along with this program; if not, see <http://www.gnu.org/licenses/>.
19 //
20 //----------------------------------------------------------------------
21 package org.perfectjpattern.core.api.behavioral.command;
22
23 import org.perfectjpattern.core.api.creational.singleton.ISingleton;
24
25 /**
26 * Null Object Pattern implementation of Command <code>Result</code>.
27 * Prevents different <code>Receiver</code> implementations from pushing
28 * <code>null</code> back into the <code>Command</code>'s result value.
29 * <br/><br/>
30 * <code>NullResult</code> is a Singleton therefore it can not be directly
31 * instantiated, neither it may be extended.
32 * <br/><br/>
33 *
34 * @author <a href="mailto:bravegag@hotmail.com">Giovanni Azua</a>
35 * @version $Revision: 1.0 $ $Date: Jun 19, 2007 10:17:38 PM $
36 */
37 public final
38 class NullResult
39 implements ISingleton
40 {
41 //------------------------------------------------------------------------
42 // public
43 //------------------------------------------------------------------------
44 /**
45 * Returns Singleton instance of <code>NullResult</code>.
46 *
47 * @return Singleton instance of <code>NullResult</code>.
48 */
49 public static NullResult
50 getInstance()
51 {
52 return INSTANCE;
53 }
54
55 //------------------------------------------------------------------------
56 // private
57 //------------------------------------------------------------------------
58 private
59 NullResult()
60 {
61 // do nothing
62 }
63
64 //------------------------------------------------------------------------
65 // members
66 //------------------------------------------------------------------------
67 /**
68 * Singleton instance of <code>NullResult</code>
69 */
70 private static final NullResult INSTANCE = new NullResult();
71 }