Index: org/apache/lucene/search/FilteredDocIdSet.java
===================================================================
--- org/apache/lucene/search/FilteredDocIdSet.java	(revision 0)
+++ org/apache/lucene/search/FilteredDocIdSet.java	(revision 0)
@@ -0,0 +1,20 @@
+package org.apache.lucene.search;
+
+public abstract class FilteredDocIdSet extends DocIdSet{
+  private final DocIdSet _innerSet;
+  public FilteredDocIdSet(DocIdSet innerSet){
+    _innerSet = innerSet;
+  }
+	
+  protected abstract boolean match(int docid);
+	
+  @Override
+  public DocIdSetIterator iterator() {
+    return new FilteredDocIdSetIterator(_innerSet.iterator()){
+      protected boolean match(int docid)
+      {
+        return FilteredDocIdSet.this.match(docid);
+      }
+    };
+  }
+}
Index: org/apache/lucene/search/FilteredDocIdSetIterator.java
===================================================================
--- org/apache/lucene/search/FilteredDocIdSetIterator.java	(revision 0)
+++ org/apache/lucene/search/FilteredDocIdSetIterator.java	(revision 0)
@@ -0,0 +1,55 @@
+package org.apache.lucene.search;
+
+import java.io.IOException;
+
+public abstract class FilteredDocIdSetIterator extends DocIdSetIterator{
+  protected DocIdSetIterator _innerIter;
+  private int _currentDoc;
+	
+  public FilteredDocIdSetIterator(DocIdSetIterator innerIter){
+    if (innerIter == null){
+      throw new IllegalArgumentException("null iterator");
+    }
+    _innerIter=innerIter;
+    _currentDoc=-1;
+  }
+	
+  abstract protected boolean match(int doc);
+	
+  public final int doc() {
+    return _currentDoc;
+  }
+
+  public final boolean next() throws IOException{
+    while(_innerIter.next()){
+      int doc=_innerIter.doc();
+      if (match(doc)){
+        _currentDoc=doc;
+        return true;
+      }
+    }
+    return false;
+  }
+
+  public final boolean skipTo(int n) throws IOException{
+    boolean flag=_innerIter.skipTo(n);
+    if (flag){
+      int doc=_innerIter.doc();
+      if (match(doc)){
+        _currentDoc=doc;
+        return true;
+      }
+      else{
+        while(_innerIter.next()){
+          int docid=_innerIter.doc();
+          if (match(docid)){
+        	_currentDoc=docid;
+            return true;
+          }
+        }
+        return false;
+      }
+    }
+    return flag;
+  }
+}