RE: Newbie query for JAVA on AS400

["Joe Pluta" <joepluta@xxxxxxxxxxxxxxxxx>]

Hi Kelly!

I posted recently on MIDRANGE-L that the CRTJVAPGM has been deprecated.

Blair Wyman's presentation to COMMON Europe last year:

http://common-es.info/files/RoadShow2005/JavaPerformance.pdf

In it, Blair says specifically (slide 23) that there are two modes:
java.compiler=jitc and java.compiler=jitc_de.  The second one is the "Direct
Execution" mode which requires CRTJVAPGM to be run on the JAR files; this is
generally slower than the other setting, which uses the JIT compiler, and
has been since V5R2.

Since CRTJVAPGM is pretty much the only optimization we programmers can do,
this implies that we really don't need to compile or optimize Java classes
on the iSeries.

The jt400Native.jar file is a little different; that's optimized to bypass
some of the sockets stuff used to access the various iSeries servers as well
as taking advantage of the current job and user the JVM is running under, so
it's always best to use that particular JAR file when appropriate.  I would
NOT, however, optimize the JAR using CRTJVAPGM; I'd let the JIT compiler do
what it is so very good at.

Joe

> From: Kelly Cookson
> 
> If you plan to run Java on the iSeries, you may want to store .java source
> files in the IFS so you can run iSeries optimizations when you compile
> them into classes. I believe IBM has already optimized parts of the
> Toolbox for Java for use on the iSeries, though I am not familiar with
> running Toolbox for Java classes on the iSeries.