The option `-XX:+UseEmptySlotsInSupers` has been deprecated in JDK 23 and will become obsolete in JDK 24. The default value is "true". This means that the HotSpot JVM will always allocate fields in a super class during field layout where there is aligned space to fit the fields. Code that relies on the position of instance fields should be aware of this detail of instance field layout. The JVM field layout format is not specified by the JVMLS and is subject to change.