RFR: 8265899: Use pattern matching for instanceof at module jdk.compiler(part 1) [v2]

[Maurizio Cimadamore]

On Mon, 26 Apr 2021 15:28:40 GMT, Guoxiong Li <gli at openjdk.org> wrote:

>> src/jdk.compiler/share/classes/com/sun/tools/javac/file/JavacFileManager.java line 963:
>> 
>>> 961:         ArrayList<PathFileObject> result;
>>> 962:         if (paths != null) {
>>> 963:             result = new ArrayList<>(paths.size());
>> 
>> This seems odd in the original code - I'd rather have somebody versed in the API double check this - @jonathan-gibbons  ? Anyway - this doesn't seem to be related with using pattern matching, so perhaps it's preferrable to just move it out of this PR.
>
> I think that removing the unnecessary `instanceof` expressions is also the goal of this cleanup. So I want to keep it.
> 
> In this case, my logical analysis is shown below.
> 
> 1. Please see the code below. The parameter type of the method `getJavaFileObjectsFromPaths` is `Collection<? extends Path>`, so we don't need to use `paths instanceof Collection<?>`. We only need to judge whether `paths` is `null`. So I use `paths != null` instead.
> 
> 
>     public Iterable<? extends JavaFileObject> getJavaFileObjectsFromPaths(
>         Collection<? extends Path> paths)
> 
> 
> 2. Because the `paths` may be `null`, I move the following code from top scope to `if (paths != null) ` branch scope to avoid the NPE.
> 
> 
>         for (Path p: paths)
>             result.add(PathFileObject.forSimplePath(this,
>                     fsInfo.getCanonicalFile(p), p));
> 
> 
> In my opinion, these two steps are reasonable for removing the `instanceof` expression.

OK

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PR: https://git.openjdk.java.net/jdk/pull/3673