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 " + property + "() on null object"); 085 } 086 087 /** 088 * @param property - the property to set 089 * @returns a NPE 090 **/ 091 public Object setProperty(String property) { 092 throw new NullPointerException("Cannot set property " + property + "() on null object"); 093 } 094 095 /** 096 * @param name the name of the method to invoke 097 * @param args - arguments to the method 098 * @returns a NPE 099 * 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 }