content: package org.apache.lucene.search;
  /**
   * Copyright 2007 The Apache Software Foundation
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  import org.apache.lucene.index.IndexReader;
  
  import java.io.IOException;
  
  /** Abstract base class providing a mechanism to restrict searches to a subset
   of an index and also maintains and returns position information.
  
   This is useful if you want to compare the positions from a SpanQuery with the positions of items in
   a filter.  For instance, if you had a SpanFilter that marked all the occurrences of the word "foo" in documents,
   and then you entered a new SpanQuery containing bar, you could not only filter by the word foo, but you could
   then compare position information for post processing.
   */
  public abstract class SpanFilter extends Filter{
    /** Returns a SpanFilterResult with true for documents which should be permitted in
      search results, and false for those that should not and Spans for where the true docs match.
     * @param reader The {@link org.apache.lucene.index.IndexReader} to load position and DocIdSet information from
     * @return A {@link SpanFilterResult}
     * @throws java.io.IOException if there was an issue accessing the necessary information
     * */
    public abstract SpanFilterResult bitSpans(IndexReader reader) throws IOException;
  }
  