Re: Anyone understand method invocation in Java?
Andreas Leitgeb wrote:
My understanding was:
interface I1 {}
interface I2 {}
interface I3 {}
class C implements I1,I2,I3 {}
abstract class MyClass {
abstract int foo(I1 i);
abstract int foo(I2 i);
int foo(I3 i) { i=null; } // just dummy code
static void bar(C c) { foo(c); }
}
According to the spec, bar(C) would always call foo(I3), not
even considering foo(I1..2) beyond that paragraph.
No. You've missed the key part. This is the concerned section in full:
# If all the maximally specific methods have override-equivalent
(?8.4.2) signatures, then:
* If exactly one of the maximally specific methods is not declared
abstract, it is the most specific method.
* Otherwise, if all the maximally specific methods are declared
abstract, and the signatures of all of the maximally specific methods
have the same erasure (?4.6), then the most specific method is chosen
arbitrarily among the subset of the maximally specific methods that have
the most specific return type. However, the most specific method is
considered to throw a checked exception if and only if that exception or
its erasure is declared in the throws clauses of each of the maximally
specific methods.
# Otherwise, we say that the method invocation is ambiguous, and a
compile-time error occurs.
The confusing clause is only invoked when the methods are
override-equivalent, that is, they have the same type parameters after
erasure.
That's why it's hard for me to come up with good cases, because the
compiler heads you off as much as possible.
--
Beware of bugs in the above code; I have only proved it correct, not
tried it. -- Donald E. Knuth