public interface ProductPort {//other names are possible - for example you might not need the 'Port' suffix
  YourResultType someFunctionalityOfProduct(Arguments here);
  //possibly other methods
}

public interface ProductPort {//other names are possible - for example you might not need the 'Port' suffix
  YourResultType someFunctionalityOfProduct(Arguments here);
  //possibly other methods
}

private final ProductPort product;//you can inject this via DI or whatever

void doSomething(){
  YourResultType result = someFunctionalityOfProduct(...);
}

private final ProductPort product;//you can inject this via DI or whatever

void doSomething(){
  YourResultType result = someFunctionalityOfProduct(...);
}