Question

The class Object contains the following method:

public final Class<? extends Object> getClass().

why the return type of this method is Class<? extends Object>

Answer 1

Because Java lacks self types. (If it had them, then the return type would be Class<? extends self_type>). So the signature merely declares Class<?>, the (next) best it can do, which is less than ideal – the compiler certainly knows that getClass() doesn’t return any class, but a class that is a subtype of the static type of the expression on which getClass() is invoked.

Thus we have this singularity, where the signature of the method declares Class<?> because of limitations of the language, but the compiler treats the return value as Class<? extends TheClass> because it knows it is safe and wants to be helpful 🙂

PS: you saw Class<? extends Object> because you called getClass() on an expression with the static type of Object.