diff --git a/src/java/org/apache/lucene/search/EmptyDocIdSetIterator.java b/src/java/org/apache/lucene/search/EmptyDocIdSetIterator.java new file mode 100644 index 00000000000..5bd15f0228a --- /dev/null +++ b/src/java/org/apache/lucene/search/EmptyDocIdSetIterator.java @@ -0,0 +1,42 @@ +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; + +/** + * An empty implementation for {@link DocIdSetIterator}. This can be used by + * classes which receive a null {@link DocIdSet} from + * {@link Filter#getDocIdSet(org.apache.lucene.index.IndexReader)}. + */ +public final class EmptyDocIdSetIterator extends DocIdSetIterator { + + private static final DocIdSetIterator instance = new EmptyDocIdSetIterator(); + + public static DocIdSetIterator getInstance() { return instance; } + + // to prevent instantiation + private EmptyDocIdSetIterator() { } + + public int advance(int target) throws IOException { return NO_MORE_DOCS; } + + public int docID() { return NO_MORE_DOCS; } + + public int nextDoc() throws IOException { return NO_MORE_DOCS; } + +}