RFR: Extend API to support JOL IntelliJ Idea plugin

[Sergey Ponomarev]

On Thu, 1 Oct 2020 07:40:09 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> [JOL Intellij Idea Plugin](https://github.com/stokito/IdeaJol)  internally uses JOL.
>> Internally in the
>> [PsiClassAdapter](https://github.com/stokito/IdeaJol/blob/master/src/main/java/com/github/stokito/IdeaJol/PsiClassAdapter.java)
>> it makes exactly the same as `org.openjdk.jol.info.ClassData#parse` but it creates the ClassData from Idea's AST/Psi
>> tree instead of raw `Class`. Unfortunately to be able to do this we need to extend API a little bit.  Here is a short
>> list of changes that I did: 1. Added an overloaded method ClassData.addSuperClassData(ClassData) so I can create an
>> instance of `ClassData`  2. Added `lossesInternal`, `lossesExternal` and `lossesTotal` fields to `ClassLayout` so they
>> calculated only once on instance creation and then can be accessed multiple times via geters by JTable  3.
>> `FieldData.create()` internally evaluate if the field is contended but we do this based on Psi tree. So we need to open
>> and make public the `FieldData` constructor.
>
> Looks sensible. Please rename the PR to e.g. "Extend API to support JOL IntelliJ Idea plugin"?

I fixed all your review comments but I wondered that I'm not listed as signed OCA. I'll sign it again but this may take
for weeks

> jol-core/src/main/java/org/openjdk/jol/info/ClassLayout.java line 145:
> 
>> 143:         }
>> 144:         long lossesExternal = instanceSize != nextFree ? instanceSize - nextFree : 0;
>> 145:         long lossesTotal = lossesInternal + lossesExternal;
> 
> I think this whole block would be more readable if we shorten the variable names.
> 
>         long next = headerSize;
>         long internal = 0;
>         for (FieldLayout fl : fields) {
>             if (fl.offset() > nextFree) {
>                 internal += fl.offset() - nextFree;
>             }
>             next = fl.offset() + fl.size();
>         }
>         long external = (instanceSize != next) ? (instanceSize - next) : 0;
>         long total = internal + external;

ok, I just kept original variable names for more clear history

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PR: https://git.openjdk.java.net/jol/pull/4