/**
    * 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.
   */
  package org.apache.hadoop.hbase.io.hfile;
  
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.io.HeapSize;
  import org.apache.hadoop.hbase.util.Bytes;
  import org.apache.hadoop.hbase.util.ClassSize;
  
  /**
   * Cache Key for use with implementations of {@link BlockCache}
   */
  @InterfaceAudience.Private
  public class BlockCacheKey implements HeapSize, java.io.Serializable {
    private static final long serialVersionUID = -5199992013113130534L;
    private final String hfileName;
    private final long offset;
  
    /**
     * Construct a new BlockCacheKey
     * @param hfileName The name of the HFile this block belongs to.
     * @param offset Offset of the block into the file
     */
    public BlockCacheKey(String hfileName, long offset) {
      this.hfileName = hfileName;
      this.offset = offset;
    }
  
    @Override
    public int hashCode() {
      return hfileName.hashCode() * 127 + (int) (offset ^ (offset >>> 32));
    }
  
    @Override
    public boolean equals(Object o) {
      if (o instanceof BlockCacheKey) {
        BlockCacheKey k = (BlockCacheKey) o;
        return offset == k.offset
            && (hfileName == null ? k.hfileName == null : hfileName
                .equals(k.hfileName));
      } else {
        return false;
      }
    }
  
    @Override
    public String toString() {
      return String.format("%s_%d", hfileName, offset);
    }
  
    public static final long FIXED_OVERHEAD = ClassSize.align(ClassSize.OBJECT +
            ClassSize.REFERENCE + // this.hfileName
            Bytes.SIZEOF_LONG);    // this.offset
  
    /**
     * Strings have two bytes per character due to default Java Unicode encoding
     * (hence length times 2).
     */
    @Override
    public long heapSize() {
      return ClassSize.align(FIXED_OVERHEAD + ClassSize.STRING +
              2 * hfileName.length());
    }
  
    // can't avoid this unfortunately
    /**
     * @return The hfileName portion of this cache key
     */
    public String getHfileName() {
      return hfileName;
    }
  
    public long getOffset() {
      return offset;
    }
  }