1 /*
2 $Id: NullObject.java 4240 2006-11-16 10:47:28Z blackdrag $
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 java.util.Collections;
49 import java.util.Iterator;
50
51 import groovy.lang.GroovyObjectSupport;
52
53 public class NullObject extends GroovyObjectSupport {
54 private static NullObject ref;
55
56 /***
57 * private constructor
58 **/
59 private NullObject() {
60 }
61
62 /***
63 * get the NullObject reference
64 **/
65 public synchronized static NullObject getNullObject() {
66 if (ref == null)
67 ref = new NullObject();
68 return ref;
69 }
70
71 /***
72 * Since this is implemented as a singleton, we should avoid the
73 * use of the clone method
74 **/
75 public Object clone() throws CloneNotSupportedException {
76 throw new CloneNotSupportedException();
77 }
78
79 /***
80 * @param property - the property to get
81 * @returns a NPE
82 **/
83 public Object getProperty(String property) {
84 throw new NullPointerException("Cannot get property " + property + "() on null object");
85 }
86
87 /***
88 * @param property - the property to set
89 * @returns a NPE
90 **/
91 public Object setProperty(String property) {
92 throw new NullPointerException("Cannot set property " + property + "() on null object");
93 }
94
95 /***
96 * @param name the name of the method to invoke
97 * @param args - arguments to the method
98 * @returns a NPE
99 *
100 **/
101 public Object invokeMethod(String name, Object args) {
102 throw new NullPointerException("Cannot invoke method " + name + "() on null object");
103 }
104
105 /***
106 * @param to - the reference object with which to compare
107 * @returns - true if this object is the same as the to argument
108 **/
109 public boolean equals(Object to) {
110 return to == null;
111 }
112
113 /***
114 * iterator() method to be able to iterate on null.
115 * Note: this part is from Invoker
116 * @return an iterator for an empty list
117 */
118 public Iterator iterator() {
119 return Collections.EMPTY_LIST.iterator();
120 }
121
122 public Object plus(String s){
123 return "null"+s;
124 }
125
126 }