1 /*
2  * Licensed to the Apache Software Foundation (ASF) under one
3  * or more contributor license agreements. See the NOTICE file
4  * distributed with this work for additional information
5  * regarding copyright ownership. The ASF licenses this file
6  * to you under the Apache License, Version 2.0 (the  "License");
7  * you may not use this file except in compliance with the License.
8  * You may obtain a copy of the License at
9  *
10  *     http://www.apache.org/licenses/LICENSE-2.0
11  *
12  * Unless required by applicable law or agreed to in writing, software
13  * distributed under the License is distributed on an "AS IS" BASIS,
14  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15  * See the License for the specific language governing permissions and
16  * limitations under the License.
17  */
18 /*
19  * $Id: XNull.java 468655 2006-10-28 07:12:06Z minchau $
20  */
21 package org.apache.xpath.objects;
22 
23 import org.apache.xml.dtm.DTM;
24 import org.apache.xpath.XPathContext;
25 
26 /**
27  * This class represents an XPath null object, and is capable of
28  * converting the null to other types, such as a string.
29  * @xsl.usage general
30  */
31 public class XNull extends XNodeSet
32 {
33     static final long serialVersionUID = -6841683711458983005L;
34 
35   /**
36    * Create an XObject.
37    */
XNull()38   public XNull()
39   {
40     super();
41   }
42 
43   /**
44    * Tell what kind of class this is.
45    *
46    * @return type CLASS_NULL
47    */
getType()48   public int getType()
49   {
50     return CLASS_NULL;
51   }
52 
53   /**
54    * Given a request type, return the equivalent string.
55    * For diagnostic purposes.
56    *
57    * @return type string "#CLASS_NULL"
58    */
getTypeString()59   public String getTypeString()
60   {
61     return "#CLASS_NULL";
62   }
63 
64   /**
65    * Cast result object to a number.
66    *
67    * @return 0.0
68    */
69 
num()70   public double num()
71   {
72     return 0.0;
73   }
74 
75   /**
76    * Cast result object to a boolean.
77    *
78    * @return false
79    */
bool()80   public boolean bool()
81   {
82     return false;
83   }
84 
85   /**
86    * Cast result object to a string.
87    *
88    * @return empty string ""
89    */
str()90   public String str()
91   {
92     return "";
93   }
94 
95   /**
96    * Cast result object to a result tree fragment.
97    *
98    * @param support XPath context to use for the conversion
99    *
100    * @return The object as a result tree fragment.
101    */
rtf(XPathContext support)102   public int rtf(XPathContext support)
103   {
104     // DTM frag = support.createDocumentFragment();
105     // %REVIEW%
106     return DTM.NULL;
107   }
108 
109 //  /**
110 //   * Cast result object to a nodelist.
111 //   *
112 //   * @return null
113 //   */
114 //  public DTMIterator iter()
115 //  {
116 //    return null;
117 //  }
118 
119   /**
120    * Tell if two objects are functionally equal.
121    *
122    * @param obj2 Object to compare this to
123    *
124    * @return True if the given object is of type CLASS_NULL
125    */
equals(XObject obj2)126   public boolean equals(XObject obj2)
127   {
128     return obj2.getType() == CLASS_NULL;
129   }
130 }
131