beagled/Lucene.Net/Search/FilteredTermEnum.cs

   1 /*
   2  * Copyright 2004 The Apache Software Foundation
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at
   7  *
   8  * http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16
  17 using System;
  18 using Term = Lucene.Net.Index.Term;
  19 using TermEnum = Lucene.Net.Index.TermEnum;
  20
  21 namespace Lucene.Net.Search
  22 {
  23
  24         /// <summary>Abstract class for enumerating a subset of all terms.
  25         /// <p>Term enumerations are always ordered by Term.compareTo().  Each term in
  26         /// the enumeration is greater than all that precede it.
  27         /// </summary>
  28         public abstract class FilteredTermEnum:TermEnum
  29         {
  30                 private Term currentTerm = null;
  31                 private TermEnum actualEnum = null;
  32
  33                 public FilteredTermEnum()
  34                 {
  35                 }
  36
  37                 /// <summary>Equality compare on the term </summary>
  38                 protected internal abstract bool TermCompare(Term term);
  39
  40                 /// <summary>Equality measure on the term </summary>
  41                 public abstract float Difference();
  42
  43                 /// <summary>Indiciates the end of the enumeration has been reached </summary>
  44                 public abstract bool EndEnum();
  45
  46                 protected internal virtual void  SetEnum(TermEnum actualEnum)
  47                 {
  48                         this.actualEnum = actualEnum;
  49                         // Find the first term that matches
  50                         Term term = actualEnum.Term();
  51                         if (term != null && TermCompare(term))
  52                                 currentTerm = term;
  53                         else
  54                                 Next();
  55                 }
  56
  57                 /// <summary> Returns the docFreq of the current Term in the enumeration.
  58                 /// Returns -1 if no Term matches or all terms have been enumerated.
  59                 /// </summary>
  60                 public override int DocFreq()
  61                 {
  62                         if (actualEnum == null)
  63                                 return - 1;
  64                         return actualEnum.DocFreq();
  65                 }
  66
  67                 /// <summary>Increments the enumeration to the next element.  True if one exists. </summary>
  68                 public override bool Next()
  69                 {
  70                         if (actualEnum == null)
  71                                 return false; // the actual enumerator is not initialized!
  72                         currentTerm = null;
  73                         while (currentTerm == null)
  74                         {
  75                                 if (EndEnum())
  76                                         return false;
  77                                 if (actualEnum.Next())
  78                                 {
  79                                         Term term = actualEnum.Term();
  80                                         if (TermCompare(term))
  81                                         {
  82                                                 currentTerm = term;
  83                                                 return true;
  84                                         }
  85                                 }
  86                                 else
  87                                         return false;
  88                         }
  89                         currentTerm = null;
  90                         return false;
  91                 }
  92
  93                 /// <summary>Returns the current Term in the enumeration.
  94                 /// Returns null if no Term matches or all terms have been enumerated.
  95                 /// </summary>
  96                 public override Term Term()
  97                 {
  98                         return currentTerm;
  99                 }
 100
 101                 /// <summary>Closes the enumeration to further activity, freeing resources.  </summary>
 102                 public override void  Close()
 103                 {
 104                         actualEnum.Close();
 105                         currentTerm = null;
 106                         actualEnum = null;
 107                 }
 108         }
 109 }