@Override
    int oopSize() {
      // Unsafe.addressSize() returns 8, even with CompressedOops. This is how many bytes each
      // element is allocated in an Object[].
      return ARRAY_OBJECT_INDEX_SCALE;
    }
UnsafeLayout uses Unsafe to guesstimate the object-layout related parameters like object header
sizes and oop sizes See HBASE-15950.
hbase-common/src/main/java/org/apache/hadoop/hbase/util/ClassSize.java