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()
| ^