module/bootclass troubles with jdk9

[Alex Buckley]

On 2/3/2015 12:18 PM, Martin Buchholz wrote:
> I read JEP 8058150 <http://openjdk.java.net/jeps/8058150> with interest.  I
> agree with the goals.  It's nice to be able to compile for a previous
> version of the platform with a single flag and without having an actual
> copy of the previous jdk available at compile time.  One idea is to promote
> javadoc tag @since to be a proper class retention annotation indicating
> when that API became available.  This would allow you to implement
> -platform N fairly cheaply, and the information would be useful elsewhere.
>
> But ... there has been an increased diversity of java runtimes lately, and
> the jigsaw project will only increase that diversity.  I think it will also
> be useful to assert that a java compilation is targeting a particular java
> runtime (or the intersection of multiple such!) given as a root directory
> of an actual JRE, and have javac deduce -source -target and -bootclasspath
> from that.  There's a whole javac target constraint algebra behind that!
> Difficult.

It is not envisaged that the target runtime image (or equivalent 
directories) contains platform classes from more than one SE release:

http://openjdk.java.net/projects/jigsaw/goals-reqs/03#mix-and-match

> Also difficult is the distinction between bootmodules and extmodules.

That shouldn't affect compilation, only execution.

Alex