@Override
  public boolean equals(Object obj) {
    if (this == obj) {
      return true;
    }
    if (obj == null || getClass() != obj.getClass()) {
      return false;
    }
    LruCachedBlock other = (LruCachedBlock) obj;
    return compareTo(other) == 0;
  }
Returns Time we were cached at in nano seconds.
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/LruCachedBlock.java