Compiling XPaths

package org.ananas.hc.compiler;

import java.util.Set;
import java.util.Vector;
import java.util.HashSet;
import java.util.Iterator;
import org.ananas.hc.QName;
import java.util.Enumeration;

public class DFAFactory
{
   public QName[] uniqueSymbols(XPathNode root)
   {
      Set qnames = new HashSet();
      uniqueSymbolsHelper(root,qnames);
      QName[] array = new QName[qnames.size()];
      return (QName[])qnames.toArray(array);
   }

   public void uniqueSymbolsHelper(XPathNode node,Set qnames)
   {
      if(node == null)
         return;
      QName qname = node.toQName();
      if(qname != null)
         qnames.add(qname);
      uniqueSymbolsHelper(node.getLeft(),qnames);
      uniqueSymbolsHelper(node.getRight(),qnames);
   }

   public DFATable createDFA(XPathNode root)
   {
      Vector dstates = new Vector(),
             dtran = new Vector(),
             astate = new Vector();
      QName[] symbols = uniqueSymbols(root);

      // initially the only unmarked state in Dstates is is firstpos(root)
      dstates.addElement(root.firstpos());

      Enumeration statesEnumeration = dstates.elements();

      // for every s as a state in dstates
      while(statesEnumeration.hasMoreElements())
      {
         Set t = (Set)statesEnumeration.nextElement();
         int dtranOfT[] = new int[symbols.length];
         dtran.addElement(dtranOfT);
         // for each input symbol a do
         for(int i = 0;i < symbols.length;i++)
         {
            // let U be the set of positions that are in followpos(p)
            // for some position p in T,
            // such that the symbol at position p is a
            Set u = e_closure(symbols[i],t);
            // if U is not empty and is not in Dstates then
            // add U as an new state to Dstates
            if (!u.isEmpty() && !dstates.contains(u))
               dstates.addElement(u);

            // Dtran[T,a] = U;
            dtranOfT[i] = dstates.indexOf(u);
         }
         astate.addElement(getAcceptingState(t));
      }

      int[][] idtran = new int[dtran.size()][symbols.length];
      dtran.copyInto(idtran);
      Object[] oastate = new Object[astate.size()];
      astate.copyInto(oastate);
      DFATable table = new DFATable(symbols,idtran,oastate);
      return table;
   }

   private Object getAcceptingState(Set t)
   {
      Iterator iterator = t.iterator();
      Object data = null;
      int priority = Integer.MIN_VALUE;
      while(iterator.hasNext())
      {
         XPathNode n = (XPathNode)iterator.next();
         if (n.getType() == XPathNode.END_MARK &&
             priority < n.getPriority())
         {
            priority = n.getPriority();
            data = n.getData();
         }
      }
      return data;
   }

   private Set e_closure(QName a,Set t)
   {
      Set result = new HashSet();
      Iterator iterator = t.iterator();
      while(iterator.hasNext())
      {
         XPathNode n = (XPathNode)iterator.next();
         if(a.matches(n))
            result.addAll(n.followpos());
      }
      return result;
   }
}