src/org/apache/xpath/objects/XNodeSet.java

/*
 * The Apache Software License, Version 1.1
 *
 *
 * Copyright (c) 1999 The Apache Software Foundation.  All rights 
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer. 
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:  
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Xalan" and "Apache Software Foundation" must
 *    not be used to endorse or promote products derived from this
 *    software without prior written permission. For written 
 *    permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache",
 *    nor may "Apache" appear in their name, without prior written
 *    permission of the Apache Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation and was
 * originally based on software copyright (c) 1999, Lotus
 * Development Corporation., http://www.lotus.com.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */
package org.apache.xpath.objects;

//import org.w3c.dom.Node;
//import org.w3c.dom.Text;
//import org.w3c.dom.DocumentFragment;
import org.apache.xml.dtm.DTM;
import org.apache.xml.dtm.DTMIterator;
import org.apache.xml.dtm.DTMManager;
import org.apache.xml.dtm.XType;
import org.apache.xml.utils.WrappedRuntimeException;
import org.apache.xml.utils.XMLString;
import org.apache.xpath.NodeSetDTM;
import org.w3c.dom.NodeList;
import org.w3c.dom.traversal.NodeIterator;

/**
 * <meta name="usage" content="general"/>
 * This class represents an XPath nodeset object, and is capable of
 * converting the nodeset to other types, such as a string.
 */
public class XNodeSet extends NodeSequence implements XSequence
{  
  XNodeSequenceSingleton m_current;
  
  
  // XNodeSetForDOM (subclass) accesses this member as NodeSetDTM
  // NodeSequence (superclass) sometimes uses it as NodeVector
  //NodeSetDTM m_obj;
  
  /**
   * Default constructor for derived objects.
   */
  /*
  protected XNodeSet()
  {
  }
  */

  /**
   * Construct a XNodeSet object.
   *
   * @param val Value of the XNodeSet object
   */
  public XNodeSet(DTMIterator val)
  {
  	if(val instanceof XNodeSet)
  	{
		// One would expect an explicit copy ctor to take precedence,
		// but apparently it doesn't always do so;
		// moving this alternative into XNodeSet(XNodeSet)
		// yields erroneous results. I don't quite understand why.

  		XNodeSet xns=(XNodeSet)val;
	    setIter(xns.m_iter);
	    m_dtmMgr = xns.m_dtmMgr;
	    m_last = xns.m_last;
	    if(!xns.hasCache())
	    	xns.setShouldCache(true);
	    m_obj = xns.m_obj;
  	}
  	else
  	{
    	setIter(val);
  		m_dtmMgr=val.getDTMManager(); // Hadn't been being done..?
  	}
  }
  
  /**
   * Construct a XNodeSet object by copying from another XNodeSet
   *
   * Currently, all copy constructions are being caught by the
   * XNodeSet(DTMIterator) ctor. I've disabled this one for
   * clarity; we should consider deleting it entirely.
   *
   * @param val Value of the XNodeSet object
   */
  /*
  public XNodeSet(XNodeSet val)
  {
  	super(val.getDTMManager());
    setIter(val.m_iter);
    m_dtmMgr = val.m_dtmMgr;
    m_last = val.m_last;
    if(!val.hasCache())
    	val.setShouldCache(true);
    m_obj = val.m_obj;
  }
  */
  
  /**
   * Passthrough for XRTreeFrag(Expression) constructor, since
   * c'tors are not inherited and there seems to be no way to 
   * invoke super.super.super().
   *
   * @param frag Document fragment this will wrap
   */
  /*
  protected XNodeSet(org.apache.xpath.Expression expr)
  {
    super(expr);
  }
  */
    
  /**
   * Construct an empty XNodeSet object.  This is used to create a mutable 
   * nodeset to which random nodes may be added.
   */
  public XNodeSet(DTMManager dtmMgr) 
  {
    this(DTM.NULL,dtmMgr);
  }

  /**
   * Construct a XNodeSet object for one node. (Or empty, if
   * the node handle is DTM.NULL.)
   *
   * @param n Handle of DTM node to add to the new XNodeSet object
   */
  public XNodeSet(int n, DTMManager dtmMgr)
  {

    super(new NodeSetDTM(dtmMgr));
    m_dtmMgr = dtmMgr;

    if (DTM.NULL != n)
    {
      ((NodeSetDTM)m_obj).addNode(n);
      m_last = 1;
    }
    else
    	m_last = 0;
  }

  /**
   * Tell that this is a CLASS_NODESET.
   *
   * @return type CLASS_NODESET
   */
  public int getType()
  {
    return CLASS_NODESET;
  }
  
  /**
   * @see org.apache.xpath.objects.XObject#getValueType()
   */
  public int getValueType()
  {
    int nodeHandle = getCurrentNode();
    if (DTM.NULL != nodeHandle)
    {
      DTM dtm = getDTM(nodeHandle);
      
      return XType.getTypeID(dtm, nodeHandle);
    }
    else
      return XType.ANYTYPE;
  }

  /**
   * Given a request type, return the equivalent string.
   * For diagnostic purposes.
   *
   * @return type string "#NODESET"
   */
  public String getTypeString()
  {
    return "#NODESET";
  }

  /**
   * Get numeric value of the string conversion from a single node.
   *
   * @param n Node to convert
   *
   * @return numeric value of the string conversion from a single node.
   */
  public double getNumberFromNode(int n)
  {
    XMLString xstr = m_dtmMgr.getDTM(n).getStringValue(n);
    return xstr.toDouble();
  }

  /**
   * Cast result object to a number.
   *
   * @return numeric value of the string conversion from the 
   * next node in the NodeSetDTM, or NAN if no node was found
   */
  public double num()
  {

    int node = item(0);
    return (node != DTM.NULL) ? getNumberFromNode(node) : Double.NaN;
  }
  
  /**
   * Cast result object to a number, but allow side effects, such as the 
   * incrementing of an iterator.
   *
   * @return numeric value of the string conversion from the 
   * next node in the NodeSetDTM, or NAN if no node was found
   */
  public double numWithSideEffects()
  {
    int node = nextNode();

    return (node != DTM.NULL) ? getNumberFromNode(node) : Double.NaN;
  }


  /**
   * Cast result object to a boolean.
   *
   * @return True if there is a next node in the nodeset
   */
  public boolean bool()
  {
    return (item(0) != DTM.NULL);
  }
  
  /**
   * Cast result object to a boolean, but allow side effects, such as the 
   * incrementing of an iterator.
   *
   * @return True if there is a next node in the nodeset
   */
  public boolean boolWithSideEffects()
  {
    return (nextNode() != DTM.NULL);
  }

  
  /**
   * Get the string conversion from a single node.
   *
   * @param n Node to convert
   *
   * @return the string conversion from a single node.
   */
  public XMLString getStringFromNode(int n)
  {
    // %OPT%
    // I guess we'll have to get a static instance of the DTM manager...
    if(DTM.NULL != n)
    {
      return m_dtmMgr.getDTM(n).getStringValue(n);
    }
    else
    {
      return org.apache.xpath.objects.XString.EMPTYSTRING;
    }
  }
  
  /**
   * Directly call the
   * characters method on the passed ContentHandler for the
   * string-value. Multiple calls to the
   * ContentHandler's characters methods may well occur for a single call to
   * this method.
   *
   * @param ch A non-null reference to a ContentHandler.
   *
   * @throws org.xml.sax.SAXException
   */
  public void dispatchCharactersEvents(org.xml.sax.ContentHandler ch)
          throws org.xml.sax.SAXException
  {
    int node = item(0);
	
    if(node != DTM.NULL)
    {
      m_dtmMgr.getDTM(node).dispatchCharactersEvents(node, ch, false);
    }
    
  }
  
  /**
   * Cast result object to an XMLString.
   *
   * @return The document fragment node data or the empty string. 
   */
  public XMLString xstr()
  {
    int node = item(0);
    return (node != DTM.NULL) ? getStringFromNode(node) : XString.EMPTYSTRING;
  }
  
  /**
   * Cast result object to a string.
   *
   * @return The string this wraps or the empty string if null
   */
  public void appendToFsb(org.apache.xml.utils.FastStringBuffer fsb)
  {
    XString xstring = (XString)xstr();
    xstring.appendToFsb(fsb);
  }
  

  /**
   * Cast result object to a string.
   *
   * @return the string conversion from the next node in the nodeset
   * or "" if there is no next node
   */
  public String str()
  {
    int node = item(0);
    return (node != DTM.NULL) ? getStringFromNode(node).toString() : "";   
  }
  
  /**
   * Return a java object that's closest to the representation
   * that should be handed to an extension.
   *
   * @return The object that this class wraps
   */
  public Object object()
  {
    if(null == m_obj)
    	return this;
    else
    	return m_obj;
  }

  // %REVIEW%
  // hmmm...
//  /**
//   * Cast result object to a result tree fragment.
//   *
//   * @param support The XPath context to use for the conversion 
//   *
//   * @return the nodeset as a result tree fragment.
//   */
//  public DocumentFragment rtree(XPathContext support)
//  {
//    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
//    DocumentBuilder db = dbf.newDocumentBuilder();
//    Document myDoc = db.newDocument();
//    
//    DocumentFragment docFrag = myDoc.createDocumentFragment();
//
//    DTMIterator nl = iter();
//    int node;
//
//    while (DTM.NULL != (node = nl.nextNode()))
//    {
//      frag.appendChild(node, true, true);
//    }
//
//    return frag.getDocument();
//  }

  /**
   * Cast result object to a nodelist.
   *
   * @return a NodeIterator.
   *
   * @throws javax.xml.transform.TransformerException
   */
  public NodeIterator nodeset() throws javax.xml.transform.TransformerException
  {
    return new org.apache.xml.dtm.ref.DTMNodeIterator(iter());
  }
  
  /**
   * Cast result object to a nodelist.
   *
   * @return a NodeList.
   *
   * @throws javax.xml.transform.TransformerException
   */
  public NodeList nodelist() throws javax.xml.transform.TransformerException
  {
    return new org.apache.xml.dtm.ref.DTMNodeList(iter());
  }

  
//  /**
//   * Return a java object that's closest to the representation
//   * that should be handed to an extension.
//   *
//   * @return The object that this class wraps
//   */
//  public Object object()
//  {
//    return new org.apache.xml.dtm.ref.DTMNodeList(iter());
//  }

  /**
   * Return the iterator without cloning, etc.
   */
  public DTMIterator iterRaw()
  {
    return this;
  }
  
  public void release(DTMIterator iter)
  {
  }
  
  /**
   * Return the sequence representing this object.
   * @return XSequence
   */
  public XSequence xseq()
  {
    return this;
  }
  
  /**
   * Cast result object to a nodelist.
   *
   * @return The nodeset as a nodelist
   */
  public DTMIterator iter()
  {
    try
    {
    	if(hasCache())
      		return cloneWithReset();
      	else
      		return this; // don't bother to clone... won't do any good!
    }
    catch (CloneNotSupportedException cnse)
    {
      throw new RuntimeException(cnse.getMessage());
    }
  }
  
  /**
   * Get a fresh copy of the object.  For use with variables.
   *
   * @return A fresh nodelist.
   */
  public XObject getFresh()
  {
    try
    {
    	if(hasCache())
      		return (XObject)cloneWithReset();
      	else
      		return this; // don't bother to clone... won't do any good!
    }
    catch (CloneNotSupportedException cnse)
    {
      throw new RuntimeException(cnse.getMessage());
    }
  }

  /**
   * Cast result object to a mutableNodeset.
   *
   * @return The nodeset as a mutableNodeset
   */
  public NodeSetDTM mutableNodeset()
  {
     NodeSetDTM mnl;
 
     if(m_obj instanceof NodeSetDTM)
     {
       mnl = (NodeSetDTM) m_obj;
     }
     else
     {
       mnl = new NodeSetDTM(iter());
       m_obj = mnl;
       setCurrentPos(0);
     }
     return mnl;  	
  }

  /** Less than comparator         */
  static LessThanComparator S_LT = new LessThanComparator();

  /** Less than or equal comparator          */
  static LessThanOrEqualComparator S_LTE = new LessThanOrEqualComparator();

  /** Greater than comparator         */
  static GreaterThanComparator S_GT = new GreaterThanComparator();

  /** Greater than or equal comparator          */
  static GreaterThanOrEqualComparator S_GTE =
    new GreaterThanOrEqualComparator();

  /** Equal comparator         */
  static EqualComparator S_EQ = new EqualComparator();

  /** Not equal comparator         */
  static NotEqualComparator S_NEQ = new NotEqualComparator();

  /**
   * Tell if one object is less than the other.
   *
   * @param obj2 Object to compare this nodeset to
   * @param comparator Comparator to use
   *
   * @return See the comments below for each object type comparison 
   *
   * @throws javax.xml.transform.TransformerException
   */
  public boolean compare(XObject obj2, Comparator comparator)
          throws javax.xml.transform.TransformerException
  {

    boolean result = false;
    int type = obj2.getType();

    if (obj2.isNodesetExpr())
    {
      // %OPT% This should be XMLString based instead of string based...

      // From http://www.w3.org/TR/xpath: 
      // If both objects to be compared are node-sets, then the comparison 
      // will be true if and only if there is a node in the first node-set 
      // and a node in the second node-set such that the result of performing 
      // the comparison on the string-values of the two nodes is true.
      // Note this little gem from the draft:
      // NOTE: If $x is bound to a node-set, then $x="foo" 
      // does not mean the same as not($x!="foo"): the former 
      // is true if and only if some node in $x has the string-value 
      // foo; the latter is true if and only if all nodes in $x have 
      // the string-value foo.
      DTMIterator list1 = iterRaw();
      DTMIterator list2 = ((XNodeSet) obj2).iterRaw();
      int node1;
      java.util.Vector node2Strings = null;

      while (DTM.NULL != (node1 = list1.nextNode()))
      {
        XMLString s1 = getStringFromNode(node1);

        if (null == node2Strings)
        {
          int node2;

          while (DTM.NULL != (node2 = list2.nextNode()))
          {
            XMLString s2 = getStringFromNode(node2);

            if (comparator.compareStrings(s1, s2))
            {
              result = true;

              break;
            }

            if (null == node2Strings)
              node2Strings = new java.util.Vector();

            node2Strings.addElement(s2);
          }
        }
        else
        {
          int n = node2Strings.size();

          for (int i = 0; i < n; i++)
          {
            if (comparator.compareStrings(s1, (XMLString)node2Strings.elementAt(i)))
            {
              result = true;

              break;
            }
          }
        }
      }
      list1.reset();
      list2.reset();
    }
    else if (XObject.CLASS_BOOLEAN == type)
    {

      // From http://www.w3.org/TR/xpath: 
      // If one object to be compared is a node-set and the other is a boolean, 
      // then the comparison will be true if and only if the result of 
      // performing the comparison on the boolean and on the result of 
      // converting the node-set to a boolean using the boolean function 
      // is true.
      double num1 = bool() ? 1.0 : 0.0;
      double num2 = obj2.num();

      result = comparator.compareNumbers(num1, num2);
    }
    else if (XObject.CLASS_NUMBER == type)
    {

      // From http://www.w3.org/TR/xpath: 
      // If one object to be compared is a node-set and the other is a number, 
      // then the comparison will be true if and only if there is a 
      // node in the node-set such that the result of performing the 
      // comparison on the number to be compared and on the result of 
      // converting the string-value of that node to a number using 
      // the number function is true. 
      DTMIterator list1 = iterRaw();
      double num2 = obj2.num();
      int node;

      while (DTM.NULL != (node = list1.nextNode()))
      {
        double num1 = getNumberFromNode(node);

        if (comparator.compareNumbers(num1, num2))
        {
          result = true;

          break;
        }
      }
      list1.reset();
    }
    else if (XObject.CLASS_RTREEFRAG == type)
    {
      XMLString s2 = obj2.xstr();
      DTMIterator list1 = iterRaw();
      int node;

      while (DTM.NULL != (node = list1.nextNode()))
      {
        XMLString s1 = getStringFromNode(node);

        if (comparator.compareStrings(s1, s2))
        {
          result = true;

          break;
        }
      }
      list1.reset();
    }
    else if (XObject.CLASS_STRING == type)
    {

      // From http://www.w3.org/TR/xpath: 
      // If one object to be compared is a node-set and the other is a 
      // string, then the comparison will be true if and only if there 
      // is a node in the node-set such that the result of performing 
      // the comparison on the string-value of the node and the other 
      // string is true. 
      XMLString s2 = obj2.xstr();
      DTMIterator list1 = iterRaw();
      int node;

      while (DTM.NULL != (node = list1.nextNode()))
      {
        XMLString s1 = getStringFromNode(node);
        if (comparator.compareStrings(s1, s2))
        {
          result = true;

          break;
        }
      }
      list1.reset();
    }
    else
    {
      result = comparator.compareNumbers(this.num(), obj2.num());
    }

    return result;
  }

  /**
   * Tell if one object is less than the other.
   *
   * @param obj2 object to compare this nodeset to
   *
   * @return see this.compare(...) 
   *
   * @throws javax.xml.transform.TransformerException
   */
  public boolean lessThan(XObject obj2) throws javax.xml.transform.TransformerException
  {
    return compare(obj2, S_LT);
  }

  /**
   * Tell if one object is less than or equal to the other.
   *
   * @param obj2 object to compare this nodeset to
   *
   * @return see this.compare(...) 
   *
   * @throws javax.xml.transform.TransformerException
   */
  public boolean lessThanOrEqual(XObject obj2) throws javax.xml.transform.TransformerException
  {
    return compare(obj2, S_LTE);
  }

  /**
   * Tell if one object is less than the other.
   *
   * @param obj2 object to compare this nodeset to
   *
   * @return see this.compare(...) 
   *
   * @throws javax.xml.transform.TransformerException
   */
  public boolean greaterThan(XObject obj2) throws javax.xml.transform.TransformerException
  {
    return compare(obj2, S_GT);
  }

  /**
   * Tell if one object is less than the other.
   *
   * @param obj2 object to compare this nodeset to
   *
   * @return see this.compare(...) 
   *
   * @throws javax.xml.transform.TransformerException
   */
  public boolean greaterThanOrEqual(XObject obj2)
          throws javax.xml.transform.TransformerException
  {
    return compare(obj2, S_GTE);
  }
  
  /**
   * Tell if two objects are functionally equal.
   *
   * @param obj2 object to compare this nodeset to
   *
   * @return see this.compare(...) 
   *
   * @throws javax.xml.transform.TransformerException
   */
  public boolean equals(XObject obj2)
  {
    int nodeHandle = obj2.getNodeHandle();
    return nodeHandle == getNodeHandle();
  }

  /**
   * Tell if two objects are functionally equal.
   *
   * @param obj2 object to compare this nodeset to
   *
   * @return see this.compare(...) 
   *
   * @throws javax.xml.transform.TransformerException
   */
  public boolean equalsExistential(XObject obj2)
  {
    try
    {
      return compare(obj2, S_EQ);
    }
    catch(javax.xml.transform.TransformerException te)
    {
      throw new org.apache.xml.utils.WrappedRuntimeException(te);
    }
  }

  /**
   * Tell if two objects are functionally not equal.
   *
   * @param obj2 object to compare this nodeset to
   *
   * @return see this.compare(...) 
   *
   * @throws javax.xml.transform.TransformerException
   */
  public boolean notEquals(XObject obj2) throws javax.xml.transform.TransformerException
  {
    return compare(obj2, S_NEQ);
  }
  
  /**
   * @see org.apache.xpath.Expression#cloneDeep()
   */
  public Object cloneDeep() throws CloneNotSupportedException
  {
    XNodeSet xns = (XNodeSet)super.clone();
    if(null != m_iter)
      xns.m_iter = (DTMIterator)m_iter.clone();
    return xns;
  }

//  /**
//   * @see org.apache.xml.dtm.DTMIterator#cloneWithReset()
//   */
//  public DTMIterator cloneWithReset() throws CloneNotSupportedException
//  {
//    DTMIterator clone = super.cloneWithReset();
//    return clone;
//  }

  /**
   * @see org.apache.xpath.objects.XSequence#getCurrent()
   */
  public XObject getCurrent()
  {
    if (null == m_current)
    {
      if (null != m_iter)
      {
        int nodeHandle = getCurrentNode();
        // I don't think it's a good idea here to have m_current 
        // get assigned, since next or previous didn't already assign it! 
        return new XNodeSequenceSingleton(
          nodeHandle,
          m_iter.getDTM(nodeHandle));
      }
      else
      {
        return null;
      }
    }
    return m_current;
  }

  /**
   * @see org.apache.xpath.objects.XSequence#getIsRandomAccess()
   */
  public boolean getIsRandomAccess()
  {
    return true; // though I'm not sure about this.
  }

  /**
   * @see org.apache.xpath.objects.XSequence#getTypeLocalName()
   */
  public String getTypeLocalName()
  {
    int nodeHandle = getCurrentNode();
    if (DTM.NULL != nodeHandle)
    {
      DTM dtm = getDTM(nodeHandle);

      return dtm.getSchemaTypeLocalName(nodeHandle);
    }
    else
      return null;
  }

  /**
   * @see org.apache.xpath.objects.XSequence#getTypeNS()
   */
  public String getTypeNS()
  {
    int nodeHandle = getCurrentNode();
    if (DTM.NULL != nodeHandle)
    {
      DTM dtm = getDTM(nodeHandle);
      return dtm.getSchemaTypeNamespace(nodeHandle);
    }
    else
      return null;
  }

  /**
   * @see org.apache.xpath.objects.XSequence#getTypes()
   */
  public int getTypes()
  {
    return XType.ANYTYPE; // don't try to predict yet.
  }

  /**
   * @see org.apache.xpath.objects.XSequence#isPureNodeSequence()
   */
  public boolean isPureNodeSequence()
  {
    return true;
  }

  /**
   * @see org.apache.xpath.objects.XSequence#isSchemaType(String, String)
   */
  public boolean isSchemaType(String namespace, String localname)
  {
    int nodeHandle = getCurrentNode();
    if (DTM.NULL != nodeHandle)
    {
      DTM dtm = getDTM(nodeHandle);
      return dtm.isNodeSchemaType(nodeHandle, namespace, localname);
    }
    else
      return false;
  }

  /**
   * @see org.apache.xpath.objects.XSequence#isSingletonOrEmpty()
   */
  public boolean isSingletonOrEmpty()
  {
    return false;
  }

  /**
   * @see org.apache.xpath.objects.XSequence#next()
   */
  public XObject next()
  {
    int node = nextNode();
    if (DTM.NULL == node)
      m_current = null;
    else
      m_current = new XNodeSequenceSingleton(node, this);
    return m_current;
  }

  /**
   * @see org.apache.xpath.objects.XSequence#previous()
   */
  public XObject previous()
  {
    int node = previousNode();
    if (DTM.NULL == node)
      m_current = null;
    else
      m_current = new XNodeSequenceSingleton(node, this);
    return m_current;
  }

  /**
   * @see org.apache.xpath.objects.XObject#isSequenceProper()
   */
  public boolean isSequenceProper()
  {
    return true;
  }


  /**
   * @see org.apache.xpath.objects.XObject#getNodeHandle()
   */
  public int getNodeHandle()
  {
    return getCurrentNode();
  }

}

/**
 * compares nodes for various boolean operations.
 */
abstract class Comparator
{

  /**
   * Compare two strings
   *
   *
   * @param s1 First string to compare
   * @param s2 Second String to compare 
   *
   * @return Whether the strings are equal or not
   */
  abstract boolean compareStrings(XMLString s1, XMLString s2);

  /**
   * Compare two numbers
   *
   *
   * @param n1 First number to compare
   * @param n2 Second number to compare
   *
   * @return Whether the numbers are equal or not
   */
  abstract boolean compareNumbers(double n1, double n2);
}

/**
 * Compare strings or numbers for less than.
 */
class LessThanComparator extends Comparator
{

  /**
   * Compare two strings for less than.
   *
   *
   * @param s1 First string to compare
   * @param s2 Second String to compare 
   *
   * @return True if s1 is less than s2
   */
  boolean compareStrings(XMLString s1, XMLString s2)
  {
    return (s1.toDouble() < s2.toDouble());
    // return s1.compareTo(s2) < 0;
  }

  /**
   * Compare two numbers for less than.
   *
   *
   * @param n1 First number to compare
   * @param n2 Second number to compare
   *
   * @return true if n1 is less than n2
   */
  boolean compareNumbers(double n1, double n2)
  {
    return n1 < n2;
  }
}

/**
 * Compare strings or numbers for less than or equal.
 */
class LessThanOrEqualComparator extends Comparator
{

  /**
   * Compare two strings for less than or equal.
   *
   *
   * @param s1 First string to compare
   * @param s2 Second String to compare
   *
   * @return true if s1 is less than or equal to s2
   */
  boolean compareStrings(XMLString s1, XMLString s2)
  {
    return (s1.toDouble() <= s2.toDouble());
    // return s1.compareTo(s2) <= 0;
  }

  /**
   * Compare two numbers for less than or equal.
   *
   *
   * @param n1 First number to compare
   * @param n2 Second number to compare
   *
   * @return true if n1 is less than or equal to n2
   */
  boolean compareNumbers(double n1, double n2)
  {
    return n1 <= n2;
  }
}

/**
 * Compare strings or numbers for greater than.
 */
class GreaterThanComparator extends Comparator
{

  /**
   * Compare two strings for greater than.
   *
   *
   * @param s1 First string to compare
   * @param s2 Second String to compare
   *
   * @return true if s1 is greater than s2
   */
  boolean compareStrings(XMLString s1, XMLString s2)
  {
    return (s1.toDouble() > s2.toDouble());
    // return s1.compareTo(s2) > 0;
  }

  /**
   * Compare two numbers for greater than.
   *
   *
   * @param n1 First number to compare
   * @param n2 Second number to compare
   *
   * @return true if n1 is greater than n2
   */
  boolean compareNumbers(double n1, double n2)
  {
    return n1 > n2;
  }
}

/**
 * Compare strings or numbers for greater than or equal.
 */
class GreaterThanOrEqualComparator extends Comparator
{

  /**
   * Compare two strings for greater than or equal.
   *
   *
   * @param s1 First string to compare
   * @param s2 Second String to compare
   *
   * @return true if s1 is greater than or equal to s2
   */
  boolean compareStrings(XMLString s1, XMLString s2)
  {
    return (s1.toDouble() >= s2.toDouble());
    // return s1.compareTo(s2) >= 0;
  }

  /**
   * Compare two numbers for greater than or equal.
   *
   *
   * @param n1 First number to compare
   * @param n2 Second number to compare
   *
   * @return true if n1 is greater than or equal to n2
   */
  boolean compareNumbers(double n1, double n2)
  {
    return n1 >= n2;
  }
}

/**
 * Compare strings or numbers for equality.
 */
class EqualComparator extends Comparator
{

  /**
   * Compare two strings for equality.
   *
   *
   * @param s1 First string to compare
   * @param s2 Second String to compare
   *
   * @return true if s1 is equal to s2
   */
  boolean compareStrings(XMLString s1, XMLString s2)
  {
    return s1.equals(s2);
  }

  /**
   * Compare two numbers for equality.
   *
   *
   * @param n1 First number to compare
   * @param n2 Second number to compare
   *
   * @return true if n1 is equal to n2
   */
  boolean compareNumbers(double n1, double n2)
  {
    return n1 == n2;
  }
}

/**
 * Compare strings or numbers for non-equality.
 */
class NotEqualComparator extends Comparator
{

  /**
   * Compare two strings for non-equality.
   *
   *
   * @param s1 First string to compare
   * @param s2 Second String to compare
   *
   * @return true if s1 is not equal to s2
   */
  boolean compareStrings(XMLString s1, XMLString s2)
  {
    return !s1.equals(s2);
  }

  /**
   * Compare two numbers for non-equality.
   *
   *
   * @param n1 First number to compare
   * @param n2 Second number to compare
   *
   * @return true if n1 is not equal to n2
   */
  boolean compareNumbers(double n1, double n2)
  {
    return n1 != n2;
  }
}