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;
/**
* 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 {
/** An empty {@code DocIdSet} instance for easy use, e.g. in Filters that hit no documents. */
public static final DocIdSet EMPTY_DOCIDSET = new DocIdSet() {
private final DocIdSetIterator iterator = new DocIdSetIterator() {
@Override
public int advance(int target) throws IOException { return NO_MORE_DOCS; }
@Override
public int docID() { return NO_MORE_DOCS; }
@Override
public int nextDoc() throws IOException { return NO_MORE_DOCS; }
};
@Override
public DocIdSetIterator iterator() {
return iterator;
}
@Override
public boolean isCacheable() {
return true;
}
};
/** Provides a {@link DocIdSetIterator} to access the set.
* This implementation can return <code>null</code> or
* <code>{@linkplain #EMPTY_DOCIDSET}.iterator()</code> if there
* are no docs that match. */
public abstract DocIdSetIterator iterator() throws IOException;
/**
* This method is a hint for {@link CachingWrapperFilter}, if this <code>DocIdSet</code>
* should be cached without copying it into a BitSet. 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</here>.
*/
public boolean isCacheable() {
return false;
}
}