フリー問題

問題文

A generic class tries to give itself a class level variable whose declared type is one of its own type parameters. Why is that declaration rejected?

選択肢

1. It is rejected because a single copy is shared by objects made from differing arguments so the compiler has nothing to settle on.
2. It is rejected because a single copy is shared by instances holding a wildcard captured at a call so the compiler has nothing to settle on.
3. It is rejected because a single copy is shared by threads running inside a pool so the compiler has nothing to settle on.
4. It is rejected because a single copy is shared by subclasses that declare a narrower bound so the compiler has nothing to settle on.