Java: Can't understand how newInstance() and getSuperClass() ,methods of Class class are working

Question

Here is example from "Java Philosophy" book (remember that FancyToy extends Toy):

Class<FancyToy> ftClass = FancyToy.class;
Class<? super FancyToy> up = ftClass.getSuperclass(); //compiles
Class<Toy> up = ftClass.getSuperclass(); //doesn't compile

Tried it in IDEA a lot of times, just have an "Incompatible types" message. Please, give me a hint, why we can't use generic type Toy only?

Thank you

Relevant https://stackoverflow.com/questions/2723397/what-is-pecs-producer-extends-consumer-super — Sotirios Delimanolis, Nov 01 '19 at 18:26

score 1 · Accepted Answer · answered Nov 01 '19 at 18:28

The direct superclass of FancyToy might be another class!

Your second line says that: it should be some class that FancyToy extends.

Whereas your third line says exactly which class is required. And either there is actually a level between Toy and FancyToy, or the compiler doesn't do the necessary type inference here.

Java: Can't understand how newInstance() and getSuperClass() ,methods of Class class are working

1 Answers1