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      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    */
     38   public XNull()
     39   {
     40     super();
     41   }
     42 
     43   /**
     44    * Tell what kind of class this is.
     45    *
     46    * @return type CLASS_NULL
     47    */
     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    */
     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 
     70   public double num()
     71   {
     72     return 0.0;
     73   }
     74 
     75   /**
     76    * Cast result object to a boolean.
     77    *
     78    * @return false
     79    */
     80   public boolean bool()
     81   {
     82     return false;
     83   }
     84 
     85   /**
     86    * Cast result object to a string.
     87    *
     88    * @return empty string ""
     89    */
     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    */
    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    */
    126   public boolean equals(XObject obj2)
    127   {
    128     return obj2.getType() == CLASS_NULL;
    129   }
    130 }
    131