JLS 9:
It is possible that the lub() function yields an infinite type. This is permissible, and a compiler for the Java programming language must recognize such situations and represent them appropriately using cyclic data structures. The possibility of an infinite type stems from the recursive calls to lub(). Readers familiar with recursive types should note that an infinite type is not the same as a recursive type.
JLS 9:
Like lub (§4.10.4), upward projection and downward projection may produce infinite types, due to the recursion on type variable bounds.