public static int memoryOverhead(Object[] objectArray) {
    if (objectArray == null) {
      return 0;
    }
    int result = getObjectHeaderSize();
    result += 4; // array length field
    result += objectArray.length * getReferenceSize();
    return roundUpSize(result);
  }
Returns the amount of memory used to store the given
object array. Note that this does not include the
memory used by objects referenced by the array.
geode-core/src/main/java/org/apache/geode/internal/JvmSizeUtils.java