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1   /*
2    $Id: NullObject.java,v 1.1 2006/06/13 22:15:02 galleon Exp $
3   
4    Copyright 2003 (C) James Strachan and Bob Mcwhirter. All Rights Reserved.
5   
6    Redistribution and use of this software and associated documentation
7    ("Software"), with or without modification, are permitted provided
8    that the following conditions are met:
9   
10   1. Redistributions of source code must retain copyright
11      statements and notices.  Redistributions must also contain a
12      copy of this document.
13  
14   2. Redistributions in binary form must reproduce the
15      above copyright notice, this list of conditions and the
16      following disclaimer in the documentation and/or other
17      materials provided with the distribution.
18  
19   3. The name "groovy" must not be used to endorse or promote
20      products derived from this Software without prior written
21      permission of The Codehaus.  For written permission,
22      please contact info@codehaus.org.
23  
24   4. Products derived from this Software may not be called "groovy"
25      nor may "groovy" appear in their names without prior written
26      permission of The Codehaus. "groovy" is a registered
27      trademark of The Codehaus.
28  
29   5. Due credit should be given to The Codehaus -
30      http://groovy.codehaus.org/
31  
32   THIS SOFTWARE IS PROVIDED BY THE CODEHAUS AND CONTRIBUTORS
33   ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
34   NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
35   FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
36   THE CODEHAUS OR ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
37   INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
38   (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
39   SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
40   HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
41   STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
42   ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
43   OF THE POSSIBILITY OF SUCH DAMAGE.
44  
45   */
46  package org.codehaus.groovy.runtime;
47  
48  import groovy.lang.GroovyObjectSupport;
49  
50  public class NullObject extends GroovyObjectSupport {
51    private static NullObject ref;
52  
53    /***
54     * private constructor
55     **/
56    private NullObject() {
57    }
58  
59    /***
60     * get the NullObject reference
61     **/
62    public synchronized static NullObject getNullObject() {
63      if (ref == null)
64        ref = new NullObject();
65      return ref;
66    }
67  
68    /***
69     * Since this is implemented as a singleton, we should avoid the 
70     * use of the clone method
71     **/
72    public Object clone() throws CloneNotSupportedException {
73      throw new CloneNotSupportedException();
74    }
75  
76    /***
77     * @param property - the property to get
78     * @returns a NPE
79     **/
80    public Object getProperty(String property) {
81      throw new NullPointerException("Cannot get property " + property + "() on null object");
82    }
83  
84    /***
85     * @param property - the property to set
86     * @returns a NPE
87     **/
88    public Object setProperty(String property) {
89      throw new NullPointerException("Cannot set property " + property + "() on null object");
90    }
91  
92    /***
93     * @param - the name of the method to invoke
94     * @param args - arguments to the method
95     * @returns a NPE
96     * 
97     **/
98    public Object invokeMethod(String name, Object args) {
99      throw new NullPointerException("Cannot invoke method " + name + "() on null object");
100   }
101 
102   /***
103    * @param to - the reference object with which to compare
104    * @returns - true if this object is the same as the to argument
105    **/
106   public boolean equals(Object to) {
107     return to == null;
108   }
109 
110   
111 }