Java Generics 和注解：类型安全

Question

I know that I can do something like:

public class AbstractDao<T extends Bean> {

}

In this case, Bean is an class or interface.

I was wondering if is there a way to do this with annotations, like:

public class AbstractDao<T extends javax.persistence.Entity> {

}

Is something like this possible?

Thanks in advance!

Answer 1

Unfortunately, there is no inheritance in annotations, so it's not possible.

Have a look at the answers to the similar question here:

Why is not possible to extend annotations in Java?

Answer 2

No. The Java Language Specification says that type variables can only be constrained to extend / implement particular classes or interfaces. Since annotating a class does not cause the class to extend or implement a particular type, you can't constrain by annotation.