Description Irfan Adilovic 2004-12-22 17:41:11 EST

Compilation of the following interface fails:
    interface I<T extends I<? super T>> {}
with:
    "Bound mismatch: The type ? super T is not a valid substitute for the
bounded parameter <T extends I<? super T>> of the type I<T>"

The compiler tries to assure that the *eventual* substitute of "? super T" is
valid by checking it against the original bound of I: "T extends I<...>".

The proper way is to check the *implementers* of this interface to assure that
their proposed type parameters are within bounds, not the bound definition
itself. The code should only fail if it could be guaranteed that no implementer
may satisfy the bounds (which is obviously not the case here)

Note 1: compiling with javac -Xlint:all gives no warnings or errors whatsoever.

Note 2: interestingly, following compiles, although it *should* be in the same
category as the code above:
    interface I<T extends I< ? extends T>> {}
Interestingly as well,
    interface I<T extends I< ? super I>> {}
compiles in contrast to javac, but
    class I<T extends I< ? super I<?>>> {}
does not compile in agreement with javac.

Node 3: Sun's javac (5.0) is problematic too, try
    interface I<T extends I<? extends I<? super T>>> {}
for a funny 1029 line long stack trace of a stack overflow.

-- Irfy