Re: <? extends String>
On 4/23/13 8:37 AM, lipska the kat wrote:
On 23/04/13 14:55, Steven Simpson wrote:
On 23/04/13 11:31, Donkey Hottie wrote:
23.04.2013 12:48, Steven Simpson kirjoitti:
public static String generateWindowsArgument(List<? extends String>
args) {
<offtopic>java.lang.String is final, so nothing can extend it.
</offtopic>
It's a matter of habit drawn from the general principle that if I don't
need to modify the list, I don't impose the additional, unnecessary
constraint on the caller, regardless of the element type.
I don't understand this. In the first place List<? extends String> says
nothing about your ability to modify the list, you can add and remove
Strings to your hearts content,
Wrong.
List<? extends String> listOfStuff = new ArrayList<String>();
listOfStuff.add("foo"); // compiler error here!
secondly the only type you can pass as
argument to generateWindowsArgument is List<String> so the construct is
redundant anyway In fact, given that >>extends String<< is effectively
meaningless I'm surprised the compiler doesn't at least issue a warning.
In general, it is only meaningless in that String cannot be extended in
the current implementation of String. As Steven pointed out, that may
not be the case for future implementations, and the compiler will never
know that.
I suppose you get away with it because compile time type erasure gets
rid of any type arguments and as there can be only one type of argument
anyway a warning would be superfluous.
Erasure is a runtime phenomenon, don't get it confused with compile-time
static type safety. the <? extends String> is an edge case that makes
less sense, but if you treat it like you'd treat any other construct,
which does no harm BTW, then you simplify your reasoning for the general
case.