org.apache.lucene.search.DocIdSet Maven / Gradle / Ivy
/*
* 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 null 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}
* does not 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;
}
}