This simple enum, although strange, is valid. In fact, this is something I get from after formatting in some jdeveloper
versions. It compiles fine but breaks on reformatting:

public enum X {
    
    A,
    B,
    ;
        private String a;
        private Class b;

        private X(String c) {
        }
        
}

Is reformatted as this (invalid, not compilable) code:

public enum x {

    A,
    B,
      ;
    private  String a;

    private  Classb ; 
    


private x(String c) {
        }
        
}