No, enums are supposed to be a complete static enumeration.
At compile time, you might want to generate your enum .java file from another source file of some sort. You could even create a .class file like this.
In some cases you might want a set of standard values but allow extension. The usual way to do this is have an interface
for the interface and an enum
that implements that interface
for the standard values. Of course, you lose the ability to switch
when you only have a reference to the interface
.