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1   /**
2    * Copyright The Apache Software Foundation
3    *
4    * Licensed to the Apache Software Foundation (ASF) under one
5    * or more contributor license agreements.  See the NOTICE file
6    * distributed with this work for additional information
7    * regarding copyright ownership.  The ASF licenses this file
8    * to you under the Apache License, Version 2.0 (the
9    * "License"); you may not use this file except in compliance
10   * with the License.  You may obtain a copy of the License at
11   *
12   *     http://www.apache.org/licenses/LICENSE-2.0
13   *
14   * Unless required by applicable law or agreed to in writing, software
15   * distributed under the License is distributed on an "AS IS" BASIS,
16   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
17   * See the License for the specific language governing permissions and
18   * limitations under the License.
19   */
20  package org.apache.hadoop.hbase.io;
21  
22  import org.apache.hadoop.classification.InterfaceAudience;
23  
24  /**
25   * Implementations can be asked for an estimate of their size in bytes.
26   * <p>
27   * Useful for sizing caches.  Its a given that implementation approximations
28   * do not account for 32 vs 64 bit nor for different VM implementations.
29   * <p>
30   * An Object's size is determined by the non-static data members in it,
31   * as well as the fixed {@link Object} overhead.
32   * <p>
33   * For example:
34   * <pre>
35   * public class SampleObject implements HeapSize {
36   *
37   *   int [] numbers;
38   *   int x;
39   * }
40   * </pre>
41   */
42  @InterfaceAudience.Private
43  public interface HeapSize {
44    /**
45     * @return Approximate 'exclusive deep size' of implementing object.  Includes
46     * count of payload and hosting object sizings.
47    */
48    long heapSize();
49  }