RFR: 8286663: Resolve IDE warnings in WTrayIconPeer and SystemTray [v3]

[Alexey Ivanov]

On Thu, 2 Jun 2022 21:48:07 GMT, Sergey Bylokhov <serb at openjdk.org> wrote:

>>> BTW I think that the usage of
>>> `return icons.toArray(EMPTY_TRAY_ARRAY);`
>>> is slower than any of other cases: presized or zero. So if we would like to use a similar pattern the zero version is better.
>> 
>> Why is it? It's the same as `icons.toArray(new TrayIcon[0])` without creating a new zero-sized array.
>
> It should be checked of course, but in zero case the size is known by the compiler not sure that in the cached case it can make the same optimizations. The article above said the cached case is a "marginal improvement over new Foo[0]"

I'm unsure if the Java compiler performs any optimisations here. The called `toArray` verifies the size first, and it's the same size either way, which is zero.

If there were no pre-allocated array, I wouldn't bother with a cached copy. But we have one. One less object to be allocated and to be garbage-collected.

Since the number of the icons is unlikely to become large, I doubt there'll be any noticeable difference.

As your sample above demonstrates, the old code could return an array with a null element in it. This is resolved by the new code.

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PR: https://git.openjdk.java.net/jdk/pull/8850