private static long estimateStringSize(final String string) {
    // each char takes 2B in Java
    return string == null ? 0 : 32 + 2L * string.length();
  }
String basic total, 32B

<ul>
  <li>Object header, 8B
  <li>char[] reference + header + length, 8 + 4 + 8= 20B
  <li>hash code, 4B
</ul>
iotdb-core/node-commons/src/main/java/org/apache/iotdb/commons/schema/MemUsageUtil.java