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;}