Java – generic type parameters depend on itself

I encountered the following situations:

I understand this:

In the type parameter part of the class, if s is the boundary of T, the type variable t depends directly on the type variable s, and if t depends directly on s or T depends directly on the type variable U, t depends on S. s (recursion uses this definition)

but

If the type variable in the type parameter part of a class depends on itself, then this is a compile - time error

What's the meaning of this? Reference

Solution

This statement means that a type parameter variable cannot depend on itself The following codes are not allowed:

class Generic<T extends T> {

}

Here t is a type parameter variable, which cannot depend on itself (direct or indirect) On the other hand, the following codes are allowed:

public class GenericRecursive<T extends GenericRecursive<T>> {

}