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package org.apache.lucene.search;
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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import java.io.IOException;
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* A DocIdSet contains a set of doc ids. Implementing classes must
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* only implement {@link #iterator} to provide access to the set.
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public abstract class DocIdSet {
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/** An empty {@code DocIdSet} instance for easy use, e.g. in Filters that hit no documents. */
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public static final DocIdSet EMPTY_DOCIDSET = new DocIdSet() {
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private final DocIdSetIterator iterator = new DocIdSetIterator() {
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public int advance(int target) throws IOException { return NO_MORE_DOCS; }
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public int docID() { return NO_MORE_DOCS; }
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public int nextDoc() throws IOException { return NO_MORE_DOCS; }
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public DocIdSetIterator iterator() {
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public boolean isCacheable() {
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/** Provides a {@link DocIdSetIterator} to access the set.
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* This implementation can return <code>null</code> or
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* <code>{@linkplain #EMPTY_DOCIDSET}.iterator()</code> if there
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* are no docs that match. */
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public abstract DocIdSetIterator iterator() throws IOException;
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* This method is a hint for {@link CachingWrapperFilter}, if this <code>DocIdSet</code>
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* should be cached without copying it into a BitSet. The default is to return
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* <code>false</code>. If you have an own <code>DocIdSet</code> implementation
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* that does its iteration very effective and fast without doing disk I/O,
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* override this method and return <code>true</here>.
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public boolean isCacheable() {