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    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 }