1 //----------------------------------------------------------------------
2 //
3 // PerfectJPattern: "Design patterns are good but components are better!"
4 // NullParameter.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>Parameter</code>.
27 * Prevents different <code>Command</code> implementations from pushing
28 * <code>null</code> into the <code>Receiver</code>'s
29 * <code>execute</code> method.
30 * <br/><br/>
31 * <code>NullParameter</code> is a Singleton therefore it can not be directly
32 * instantiated, neither it may be extended.
33 * <br/><br/>
34 *
35 * @author <a href="mailto:bravegag@hotmail.com">Giovanni Azua</a>
36 * @version $Revision: 1.0 $ $Date: Jun 19, 2007 10:17:38 PM $
37 */
38 public final
39 class NullParameter
40 implements ISingleton
41 {
42 //------------------------------------------------------------------------
43 // public
44 //------------------------------------------------------------------------
45 /**
46 * Returns Singleton instance of <code>NullParameter</code>.
47 *
48 * @return Singleton instance of <code>NullParameter</code>.
49 */
50 public static NullParameter
51 getInstance()
52 {
53 return INSTANCE;
54 }
55
56 //------------------------------------------------------------------------
57 // private
58 //------------------------------------------------------------------------
59 private
60 NullParameter()
61 {
62 // do nothing
63 }
64
65 //------------------------------------------------------------------------
66 // members
67 //------------------------------------------------------------------------
68 /**
69 * Singleton instance of <code>NullParameter</code>
70 */
71 private static final NullParameter INSTANCE = new NullParameter();
72 }