| 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; |
| import java.util.Collection; |
| import java.util.Collections; |
| |
| 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(); |
| } |
| |
| @Override |
| public boolean isCacheable() { |
| return true; |
| } |
| |
| // 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; |
| } |
| |
| /** |
| * This method is a hint for {@link CachingWrapperFilter}, if this <code>DocIdSet</code> |
| * should be cached without copying it. The default is to return |
| * <code>false</code>. If you have an own <code>DocIdSet</code> implementation |
| * that does its iteration very effective and fast without doing disk I/O, |
| * override this method and return <code>true</code>. |
| */ |
| public boolean isCacheable() { |
| return false; |
| } |
| |
| @Override |
| public Collection<Accountable> getChildResources() { |
| return Collections.emptyList(); |
| } |
| } |