| 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 { |
| |
| /** An empty {@code DocIdSetIterator} instance */ |
| public static final DocIdSetIterator empty() { |
| return new DocIdSetIterator() { |
| boolean exhausted = false; |
| |
| @Override |
| public int advance(int target) { |
| assert !exhausted; |
| assert target >= 0; |
| exhausted = true; |
| return NO_MORE_DOCS; |
| } |
| |
| @Override |
| public int docID() { |
| return exhausted ? NO_MORE_DOCS : -1; |
| } |
| @Override |
| public int nextDoc() { |
| assert !exhausted; |
| exhausted = true; |
| return NO_MORE_DOCS; |
| } |
| |
| @Override |
| public long cost() { |
| return 0; |
| } |
| }; |
| } |
| |
| /** A {@link DocIdSetIterator} that matches all documents up to |
| * {@code maxDoc - 1}. */ |
| public static final DocIdSetIterator all(final int maxDoc) { |
| return new DocIdSetIterator() { |
| int doc = -1; |
| |
| @Override |
| public int docID() { |
| return doc; |
| } |
| |
| @Override |
| public int nextDoc() throws IOException { |
| return advance(doc + 1); |
| } |
| |
| @Override |
| public int advance(int target) throws IOException { |
| doc = target; |
| if (doc >= maxDoc) { |
| doc = NO_MORE_DOCS; |
| } |
| return doc; |
| } |
| |
| @Override |
| public long cost() { |
| return maxDoc; |
| } |
| }; |
| } |
| |
| /** |
| * 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><code>-1</code> 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 the current whose document number is greater |
| * than or equal to <i>target</i>, and returns the document number itself. |
| * Exhausts the iterator and returns {@link #NO_MORE_DOCS} if <i>target</i> |
| * is greater than the highest document number in the set. |
| * <p> |
| * The behavior of this method is <b>undefined</b> when called with |
| * <code> target ≤ current</code>, or after the iterator has exhausted. |
| * Both cases may result in unpredicted behavior. |
| * <p> |
| * When <code> target > current</code> it behaves as if written: |
| * |
| * <pre class="prettyprint"> |
| * int advance(int target) { |
| * int doc; |
| * while ((doc = nextDoc()) < target) { |
| * } |
| * return doc; |
| * } |
| * </pre> |
| * |
| * Some implementations are considerably more efficient than that. |
| * <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> |
| * |
| * @since 2.9 |
| */ |
| public abstract int advance(int target) throws IOException; |
| |
| /** Slow (linear) implementation of {@link #advance} relying on |
| * {@link #nextDoc()} to advance beyond the target position. */ |
| protected final int slowAdvance(int target) throws IOException { |
| assert docID() < target; |
| int doc; |
| do { |
| doc = nextDoc(); |
| } while (doc < target); |
| return doc; |
| } |
| |
| /** |
| * Returns the estimated cost of this {@link DocIdSetIterator}. |
| * <p> |
| * This is generally an upper bound of the number of documents this iterator |
| * might match, but may be a rough heuristic, hardcoded value, or otherwise |
| * completely inaccurate. |
| */ |
| public abstract long cost(); |
| |
| } |