http://lucene.apache.org/lucene-parent/lucene-core: Apache Lucene Java Core (The Apache Software Foundation) 
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 * 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
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 */

package org.apache.lucene.search;

import org.apache.lucene.index.DocValues;
import org.apache.lucene.index.LeafReader;
import org.apache.lucene.index.LeafReaderContext;


Interface defining whether or not an object can be cached against a LeafReader Objects that depend only on segment-immutable structures such as Points or postings lists can just return true from isCacheable(LeafReaderContext) Objects that depend on doc values should return DocValues.isCacheable(LeafReaderContext, String...), which will check to see if the doc values fields have been updated. Updated doc values fields are not suitable for cacheing. Objects that are not segment-immutable, such as those that rely on global statistics or scores, should return false 
/**
 * Interface defining whether or not an object can be cached against a {@link LeafReader}
 *
 * Objects that depend only on segment-immutable structures such as Points or postings lists
 * can just return {@code true} from {@link #isCacheable(LeafReaderContext)}
 *
 * Objects that depend on doc values should return {@link DocValues#isCacheable(LeafReaderContext, String...)}, which
 * will check to see if the doc values fields have been updated.  Updated doc values fields are not suitable
 * for cacheing.
 *
 * Objects that are not segment-immutable, such as those that rely on global statistics or scores,
 * should return {@code false}
 */
public interface SegmentCacheable {

  
Returns:true if the object can be cached against a given leaf
/**
   * @return {@code true} if the object can be cached against a given leaf
   */
  boolean isCacheable(LeafReaderContext ctx);

}