Coverage Report

Coverage Report - net.wotonomy.control.EONullValue

Classes in this File

1.8

 /*
 Wotonomy: OpenStep design patterns for pure Java applications.
 Copyright (C) 2001 Intersect Software Corporation
 
 This library is free software; you can redistribute it and/or
 modify it under the terms of the GNU Lesser General Public
 License as published by the Free Software Foundation; either
 version 2.1 of the License, or (at your option) any later version.
 
 This library 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
 Lesser General Public License for more details.
 
 You should have received a copy of the GNU Lesser General Public
 License along with this library; if not, see http://www.gnu.org
 */
 
 package net.wotonomy.control;
 
 import java.io.Serializable;
 
 import net.wotonomy.foundation.NSNull;
 
 /**
 * EONullValue is used to represent null in Collections classes
 * because List and Map do not specify whether null values
 * are allowed and because NSArray and NSDictionary explicitly
 * do not allow null values. <br><br>
 *
 * Use of the static singleton method nullValue() is required 
 * by this implementation because Java cannot return a singleton
 * instance from a constructor. <br><br>
 *
 * This implementation duplicates NSNull, but the singleton instances
 * are of course different.  Be careful.  I have no idea why this
 * class was even created, given that NSNull exists.
 *
 * @author michael@mpowers.net
 * @author $Author: cgruber $
 * @version $Revision: 894 $
 */
 public class EONullValue implements Serializable
 {
     private static final EONullValue instance = new EONullValue();
     
     /**
     * Create a new instance of EONullValue.
     */
     private EONullValue ()
     {
     }
 
     /**
     * Constructor specifying name and object.
     */
     public static EONullValue nullValue ()
     {        
         return instance; 
     }
 
     /**
     * Returns a human-readable string representation.
     */
     public String toString()
     {
         return "[null]";
     }
     
     /**
     * Hashcode of all instances is zero.
     */
     public int hashCode()
     {
         return 0;   
     }
     
     /**
     * Implemented to return true for any instance of EONullValue
     * and for any instance of NSNull.
     */
     public boolean equals( Object anObject )
     {
         if ( anObject instanceof EONullValue ) return true;
         if ( anObject instanceof NSNull ) return true;
         return false;
     }
 }
 
 /*
  * $Log$
  * Revision 1.2  2006/02/16 16:47:14  cgruber
  * Move some classes in to "internal" packages and re-work imports, etc.
  *
  * Also use UnsupportedOperationExceptions where appropriate, instead of WotonomyExceptions.
  *
  * Revision 1.1  2006/02/16 13:19:57  cgruber
  * Check in all sources in eclipse-friendly maven-enabled packages.
  *
  * Revision 1.3  2003/08/06 23:07:52  chochos
  * general code cleanup (mostly, removing unused imports)
  *
  * Revision 1.2  2001/03/01 20:35:38  mpowers
  * Implemented equals and hashCode.
  *
  * Revision 1.1  2001/02/26 22:41:51  mpowers
  * Implemented null placeholder classes.
  * Duplicator now uses NSNull.
  * No longer catching base exception class.
  *
  *
  */
 

1		/*
2		Wotonomy: OpenStep design patterns for pure Java applications.
3		Copyright (C) 2001 Intersect Software Corporation
4
5		This library is free software; you can redistribute it and/or
6		modify it under the terms of the GNU Lesser General Public
7		License as published by the Free Software Foundation; either
8		version 2.1 of the License, or (at your option) any later version.
9
10		This library is distributed in the hope that it will be useful,
11		but WITHOUT ANY WARRANTY; without even the implied warranty of
12		MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13		Lesser General Public License for more details.
14
15		You should have received a copy of the GNU Lesser General Public
16		License along with this library; if not, see http://www.gnu.org
17		*/
18
19		package net.wotonomy.control;
20
21		import java.io.Serializable;
22
23		import net.wotonomy.foundation.NSNull;
24
25		/**
26		* EONullValue is used to represent null in Collections classes
27		* because List and Map do not specify whether null values
28		* are allowed and because NSArray and NSDictionary explicitly
29		* do not allow null values. <br><br>
30		*
31		* Use of the static singleton method nullValue() is required
32		* by this implementation because Java cannot return a singleton
33		* instance from a constructor. <br><br>
34		*
35		* This implementation duplicates NSNull, but the singleton instances
36		* are of course different. Be careful. I have no idea why this
37		* class was even created, given that NSNull exists.
38		*
39		* @author michael@mpowers.net
40		* @author $Author: cgruber $
41		* @version $Revision: 894 $
42		*/
43	0	public class EONullValue implements Serializable
44		{
45	0	private static final EONullValue instance = new EONullValue();
46
47		/**
48		* Create a new instance of EONullValue.
49		*/
50	0	private EONullValue ()
51	0	{
52	0	}
53
54		/**
55		* Constructor specifying name and object.
56		*/
57		public static EONullValue nullValue ()
58		{
59	0	return instance;
60		}
61
62		/**
63		* Returns a human-readable string representation.
64		*/
65		public String toString()
66		{
67	0	return "[null]";
68		}
69
70		/**
71		* Hashcode of all instances is zero.
72		*/
73		public int hashCode()
74		{
75	0	return 0;
76		}
77
78		/**
79		* Implemented to return true for any instance of EONullValue
80		* and for any instance of NSNull.
81		*/
82		public boolean equals( Object anObject )
83		{
84	0	if ( anObject instanceof EONullValue ) return true;
85	0	if ( anObject instanceof NSNull ) return true;
86	0	return false;
87		}
88		}
89
90		/*
91		* $Log$
92		* Revision 1.2 2006/02/16 16:47:14 cgruber
93		* Move some classes in to "internal" packages and re-work imports, etc.
94		*
95		* Also use UnsupportedOperationExceptions where appropriate, instead of WotonomyExceptions.
96		*
97		* Revision 1.1 2006/02/16 13:19:57 cgruber
98		* Check in all sources in eclipse-friendly maven-enabled packages.
99		*
100		* Revision 1.3 2003/08/06 23:07:52 chochos
101		* general code cleanup (mostly, removing unused imports)
102		*
103		* Revision 1.2 2001/03/01 20:35:38 mpowers
104		* Implemented equals and hashCode.
105		*
106		* Revision 1.1 2001/02/26 22:41:51 mpowers
107		* Implemented null placeholder classes.
108		* Duplicator now uses NSNull.
109		* No longer catching base exception class.
110		*
111		*
112		*/
113