it is possible to define a sealed intf, and permitted subclass but can't be used

jshell> sealed interface Foo permits X {
   ...>     public int x();
   ...> }
|  created interface Foo, however, it cannot be referenced until class X is declaredjshell> class X implements Foo { public int x() { return 3; } }
|  created class X, however, it cannot be referenced until class Foo is declaredjshell> new X()
|  Error:
|  cannot find symbol
|    symbol:   class X
|  new X()
|      ^