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1   /**
2    * Copyright 2009 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  /**
23   * Implementations can be asked for an estimate of their size in bytes.
24   * <p>
25   * Useful for sizing caches.  Its a given that implementation approximations
26   * do not account for 32 vs 64 bit nor for different VM implementations.
27   * <p>
28   * An Object's size is determined by the non-static data members in it,
29   * as well as the fixed {@link Object} overhead.
30   * <p>
31   * For example:
32   * <pre>
33   * public class SampleObject implements HeapSize {
34   *
35   *   int [] numbers;
36   *   int x;
37   * }
38   * </pre>
39   */
40  public interface HeapSize {
41    /**
42     * @return Approximate 'exclusive deep size' of implementing object.  Includes
43     * count of payload and hosting object sizings.
44    */
45    public long heapSize();
46  
47  }