The java.lang.System has this code comment which states:



/* Register the natives via the static initializer.
     *
     * VM will invoke the initializeSystemClass method to complete
     * the initialization for this class separated from clinit.
     * Note that to use properties set by the VM, see the constraints
     * described in the initializeSystemClass method.
     */

The initializeSystemClass method is no longer existent and this comment is outdated.

As noted in the core-lib-dev discussion, this needs to be updated or removed to reflect the current state http://mail.openjdk.java.net/pipermail/core-libs-dev/2019-October/062947.html