On Wed, 22 Sep 2021 00:21:01 GMT, Claes Redestad <redes...@openjdk.org> wrote:
>> Currently the method is implemented like
>>
>> public List<Class<?>> parameterList() {
>> return Collections.unmodifiableList(Arrays.asList(ptypes.clone()));
>> }
>>
>> This seems to be excessive, as three objects are allocated here. Instead we
>> can use `List.of(ptypes)` which doesn't allocate anything for empty array
>> and for one of length 1 and 2 it allocates lightweight objects with 2
>> fields, still copying longer arrays. This is likely to be fruitful as most
>> of methods have 0-2 parameters.
>>
>> Also there is a couple of cases when `MethodType.parameterLis()` is called
>> to get its size, which is excessive either as we can use
>> `MethodType.parameterCount()` instead.
>
> This change introduces a subtle behavior change in that `List.of` produce a
> `null`-hostile list, for example `list.contains(null)` will throw NPE. Does
> this need to be spelled out? (FTR I think such null-hostile behavior should
> be reconsidered)
> @cl4es null-issue was the one I was afraid most of all in this case. I think
> that the initial array `ptypes` never contains null elements due to it's
> business meaning (we cannot have a param without type). Also we do explicit
> null-check in `checkPtypes()` method, called from `makeImpl()`.
No, on the producer side there's no issue since a parameter type can't be
`null`. The compatibility issue I have in mind is only the (very minor) issue
that the returned list would now throw NPE if you call
`mt.parameterList().contains(null)` where it before would just return `false`.
I don't think this is a real issue, but the subtle behavior change might
warrant a CSR to document the stricter behavior.
-------------
PR: https://git.openjdk.java.net/jdk/pull/5489
