Question

Hi I’m writing the reporting system and want to make end-user specify type if he extends my class.

class A <T extends C>
{...}

class B extends A // Compile error
{...}

class B extends A<D> // Compile error
{...}

class B extends A<C> // Success

Is that possible?

Answer 1

class B extends A // Compile error

No, for the sake of backwards compatibility, generics in Java are optional. You cannot force the programmer to use them. This will only generate a warning (“do not use raw types”).

 class B extends A<D>  // compile error

If they do use generics, they have to be correct, though. In the case that D does not match the specification, this will be a compiler error.