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;
  
  /**
   * This abstract class defines methods to iterate over a set of non-decreasing
   * doc ids. Note that this class assumes it iterates on doc Ids, and therefore
   * {@link #NO_MORE_DOCS} is set to {@value #NO_MORE_DOCS} in order to be used as
   * a sentinel object. Implementations of this class are expected to consider
   * {@link Integer#MAX_VALUE} as an invalid value.
   */
  public abstract class DocIdSetIterator {
    
    /**
     * When returned by {@link #nextDoc()}, {@link #advance(int)} and
     * {@link #docID()} it means there are no more docs in the iterator.
     */
    public static final int NO_MORE_DOCS = Integer.MAX_VALUE;
  
    /**
     * Returns the following:
     * <ul>
     * <li>-1 or {@link #NO_MORE_DOCS} if {@link #nextDoc()} or
     * {@link #advance(int)} were not called yet.
     * <li>{@link #NO_MORE_DOCS} if the iterator has exhausted.
     * <li>Otherwise it should return the doc ID it is currently on.
     * </ul>
     * <p>
     * 
     * @since 2.9
     */
    public abstract int docID();
  
    /**
     * Advances to the next document in the set and returns the doc it is
     * currently on, or {@link #NO_MORE_DOCS} if there are no more docs in the
     * set.<br>
     * 
     * <b>NOTE:</b> after the iterator has exhausted you should not call this
     * method, as it may result in unpredicted behavior.
     * 
     * @since 2.9
     */
    public abstract int nextDoc() throws IOException;
  
    /**
     * Advances to the first beyond (see NOTE below) the current whose document
     * number is greater than or equal to <i>target</i>. Returns the current
     * document number or {@link #NO_MORE_DOCS} if there are no more docs in the
     * set.
     * <p>
     * Behaves as if written:
     * 
     * <pre>
     * int advance(int target) {
     *   int doc;
     *   while ((doc = nextDoc()) &lt; target) {
     *   }
     *   return doc;
     * }
     * </pre>
     * 
     * Some implementations are considerably more efficient than that.
     * <p>
     * <b>NOTE:</b> when <code> target &le; current</code> implementations may opt
     * not to advance beyond their current {@link #docID()}.
     * <p>
     * <b>NOTE:</b> this method may be called with {@link #NO_MORE_DOCS} for
     * efficiency by some Scorers. If your implementation cannot efficiently
     * determine that it should exhaust, it is recommended that you check for that
     * value in each call to this method.
     * <p>
     * <b>NOTE:</b> after the iterator has exhausted you should not call this
     * method, as it may result in unpredicted behavior.
     * <p>
     * 
     * @since 2.9
     */
    public abstract int advance(int target) throws IOException;
  
  }
  