| /* |
| * 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. |
| */ |
| package org.apache.lucene.search; |
| |
| import java.io.IOException; |
| import org.apache.lucene.util.Accountable; |
| import org.apache.lucene.util.Bits; |
| |
| /** |
| * A DocIdSet contains a set of doc ids. Implementing classes must only implement {@link #iterator} |
| * to provide access to the set. |
| */ |
| public abstract class DocIdSet implements Accountable { |
| |
| /** An empty {@code DocIdSet} instance */ |
| public static final DocIdSet EMPTY = |
| new DocIdSet() { |
| |
| @Override |
| public DocIdSetIterator iterator() { |
| return DocIdSetIterator.empty(); |
| } |
| |
| // we explicitly provide no random access, as this filter is 100% sparse and iterator exits |
| // faster |
| @Override |
| public Bits bits() { |
| return null; |
| } |
| |
| @Override |
| public long ramBytesUsed() { |
| return 0L; |
| } |
| }; |
| |
| /** |
| * Provides a {@link DocIdSetIterator} to access the set. This implementation can return <code> |
| * null</code> if there are no docs that match. |
| */ |
| public abstract DocIdSetIterator iterator() throws IOException; |
| |
| // TODO: somehow this class should express the cost of |
| // iteration vs the cost of random access Bits; for |
| // expensive Filters (e.g. distance < 1 km) we should use |
| // bits() after all other Query/Filters have matched, but |
| // this is the opposite of what bits() is for now |
| // (down-low filtering using e.g. FixedBitSet) |
| |
| /** |
| * Optionally provides a {@link Bits} interface for random access to matching documents. |
| * |
| * @return {@code null}, if this {@code DocIdSet} does not support random access. In contrast to |
| * {@link #iterator()}, a return value of {@code null} <b>does not</b> imply that no documents |
| * match the filter! The default implementation does not provide random access, so you only |
| * need to implement this method if your DocIdSet can guarantee random access to every docid |
| * in O(1) time without external disk access (as {@link Bits} interface cannot throw {@link |
| * IOException}). This is generally true for bit sets like {@link |
| * org.apache.lucene.util.FixedBitSet}, which return itself if they are used as {@code |
| * DocIdSet}. |
| */ |
| public Bits bits() throws IOException { |
| return null; |
| } |
| } |