content: package org.apache.lucene.search;
  
  /**
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You 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 java.io.IOException;
  
  /**
   * Abstract decorator class for a DocIdSet implementation
   * that provides on-demand filtering/validation
   * mechanism on a given DocIdSet.
   *
   * <p/>
   *
   * Technically, this same functionality could be achieved
   * with ChainedFilter (under contrib/misc), however the
   * benefit of this class is it never materializes the full
   * bitset for the filter.  Instead, the {@link #match}
   * method is invoked on-demand, per docID visited during
   * searching.  If you know few docIDs will be visited, and
   * the logic behind {@link #match} is relatively costly,
   * this may be a better way to filter than ChainedFilter.
   *
   * @see DocIdSet
   */
  
  public abstract class FilteredDocIdSet extends DocIdSet {
    private final DocIdSet _innerSet;
    
    /**
     * Constructor.
     * @param innerSet Underlying DocIdSet
     */
    public FilteredDocIdSet(DocIdSet innerSet) {
      _innerSet = innerSet;
    }
    
    /** This DocIdSet implementation is cacheable if the inner set is cacheable. */
    @Override
    public boolean isCacheable() {
      return _innerSet.isCacheable();
    }
  
    /**
     * Validation method to determine whether a docid should be in the result set.
     * @param docid docid to be tested
     * @return true if input docid should be in the result set, false otherwise.
     */
    protected abstract boolean match(int docid) throws IOException;
  	
    /**
     * Implementation of the contract to build a DocIdSetIterator.
     * @see DocIdSetIterator
     * @see FilteredDocIdSetIterator
     */
    @Override
    public DocIdSetIterator iterator() throws IOException {
      return new FilteredDocIdSetIterator(_innerSet.iterator()) {
        @Override
        protected boolean match(int docid) throws IOException {
          return FilteredDocIdSet.this.match(docid);
        }
      };
    }
  }
  