JDK-6479237 has modified the format of StackTraceElement::toString. Because the values of the public fields are not sufficient to disambiguate between the different format alternatives, JDK-6479237 also introduced a non transient classOrLoaderModuleClassName field, which is used when the StackTraceElement is created by the VM when filling in a Throwable stack trace from its back trace.

When non null, this field will eventually contain the "[[class-loader-name]/[module-name[@module-version]]]" string to be used as part of the StackTraceElement::toString representation.

Instead of storing a String, this field could instead store a bitmap telling which field should be omitted from the StackTraceElement::toString representation - thus reducing the footprint of the Throwable's StackTraceElement instances.