001: /*
002: $Id: NullObject.java 4240 2006-11-16 10:47:28Z blackdrag $
003:
004: Copyright 2003 (C) James Strachan and Bob Mcwhirter. All Rights Reserved.
005:
006: Redistribution and use of this software and associated documentation
007: ("Software"), with or without modification, are permitted provided
008: that the following conditions are met:
009:
010: 1. Redistributions of source code must retain copyright
011: statements and notices. Redistributions must also contain a
012: copy of this document.
013:
014: 2. Redistributions in binary form must reproduce the
015: above copyright notice, this list of conditions and the
016: following disclaimer in the documentation and/or other
017: materials provided with the distribution.
018:
019: 3. The name "groovy" must not be used to endorse or promote
020: products derived from this Software without prior written
021: permission of The Codehaus. For written permission,
022: please contact info@codehaus.org.
023:
024: 4. Products derived from this Software may not be called "groovy"
025: nor may "groovy" appear in their names without prior written
026: permission of The Codehaus. "groovy" is a registered
027: trademark of The Codehaus.
028:
029: 5. Due credit should be given to The Codehaus -
030: http://groovy.codehaus.org/
031:
032: THIS SOFTWARE IS PROVIDED BY THE CODEHAUS AND CONTRIBUTORS
033: ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
034: NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
035: FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
036: THE CODEHAUS OR ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
037: INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
038: (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
039: SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
040: HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
041: STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
042: ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
043: OF THE POSSIBILITY OF SUCH DAMAGE.
044:
045: */
046: package org.codehaus.groovy.runtime;
047:
048: import java.util.Collections;
049: import java.util.Iterator;
050:
051: import groovy.lang.GroovyObjectSupport;
052:
053: public class NullObject extends GroovyObjectSupport {
054: private static NullObject ref;
055:
056: /**
057: * private constructor
058: **/
059: private NullObject() {
060: }
061:
062: /**
063: * get the NullObject reference
064: **/
065: public synchronized static NullObject getNullObject() {
066: if (ref == null)
067: ref = new NullObject();
068: return ref;
069: }
070:
071: /**
072: * Since this is implemented as a singleton, we should avoid the
073: * use of the clone method
074: **/
075: public Object clone() throws CloneNotSupportedException {
076: throw new CloneNotSupportedException();
077: }
078:
079: /**
080: * @param property - the property to get
081: * @returns a NPE
082: **/
083: public Object getProperty(String property) {
084: throw new NullPointerException("Cannot get property "
085: + property + "() on null object");
086: }
087:
088: /**
089: * @param property - the property to set
090: * @returns a NPE
091: **/
092: public Object setProperty(String property) {
093: throw new NullPointerException("Cannot set property "
094: + property + "() on null object");
095: }
096:
097: /**
098: * @param name the name of the method to invoke
099: * @param args - arguments to the method
100: * @returns a NPE
101: *
102: **/
103: public Object invokeMethod(String name, Object args) {
104: throw new NullPointerException("Cannot invoke method " + name
105: + "() on null object");
106: }
107:
108: /**
109: * @param to - the reference object with which to compare
110: * @returns - true if this object is the same as the to argument
111: **/
112: public boolean equals(Object to) {
113: return to == null;
114: }
115:
116: /**
117: * iterator() method to be able to iterate on null.
118: * Note: this part is from Invoker
119: * @return an iterator for an empty list
120: */
121: public Iterator iterator() {
122: return Collections.EMPTY_LIST.iterator();
123: }
124:
125: public Object plus(String s) {
126: return "null" + s;
127: }
128:
129: }
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