code: public static long shallowSizeOf(Object o) {
      Class<? extends Object> clz = o.getClass();
      if (clz.isArray()) {
        int len = Array.getLength(o);
        return regulateSize(THE_UNSAFE.arrayBaseOffset(clz) + (long) THE_UNSAFE.arrayIndexScale(clz) * len);
      }
      return shallowSizeOf(clz);
    }
docs: SHALLOW size of the given object. <br>
  If given a primitive type, the result will be incorrect.<br>
  For primitive type, use {@link UnsafeUtil#shallowSizeOf(Class)}.
  
  @param o
  @return