content: package org.apache.lucene.util;
  
  /**
   * 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.util.BitSet;
  
  import org.apache.lucene.search.DocIdSet;
  import org.apache.lucene.search.DocIdSetIterator;
  
  
  /** Simple DocIdSet and DocIdSetIterator backed by a BitSet */
  public class DocIdBitSet extends DocIdSet {
    private BitSet bitSet;
      
    public DocIdBitSet(BitSet bitSet) {
      this.bitSet = bitSet;
    }
  
    @Override
    public DocIdSetIterator iterator() {
      return new DocIdBitSetIterator(bitSet);
    }
  
    /** This DocIdSet implementation is cacheable. */
    @Override
    public boolean isCacheable() {
      return true;
    }
    
    /**
     * Returns the underlying BitSet. 
     */
    public BitSet getBitSet() {
  	return this.bitSet;
    }
    
    private static class DocIdBitSetIterator extends DocIdSetIterator {
      private int docId;
      private BitSet bitSet;
      
      DocIdBitSetIterator(BitSet bitSet) {
        this.bitSet = bitSet;
        this.docId = -1;
      }
      
      @Override
      public int docID() {
        return docId;
      }
      
      @Override
      public int nextDoc() {
        // (docId + 1) on next line requires -1 initial value for docNr:
        int d = bitSet.nextSetBit(docId + 1);
        // -1 returned by BitSet.nextSetBit() when exhausted
        docId = d == -1 ? NO_MORE_DOCS : d;
        return docId;
      }
    
      @Override
      public int advance(int target) {
        int d = bitSet.nextSetBit(target);
        // -1 returned by BitSet.nextSetBit() when exhausted
        docId = d == -1 ? NO_MORE_DOCS : d;
        return docId;
      }
    }
  }
  