Using Java methods in R

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From: marchywka at hotmail.com
To: hill0093 at umn.edu; r-help at r-project.org
Date: Sat, 23 Apr 2011 15:12:30 -0400
Subject: Re: [R] Using Java methods in R

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Date: Sat, 23 Apr 2011 05:32:59 -0700
From: hill0093 at umn.edu
To: r-help at r-project.org
Subject: Re: [R] Using Java methods in R

No answer to my post,
so let's try a simpler question. Am I doing this correctly?
I have the RGui with R Console on the screen.
On rhe top pullDowns, Packages > Install Packages > USA(IA)> rJava
library(rJava)
.jinit()
qsLin <- .jnew("C:/ad/j/CalqsLin")
Error in .jnew("C:/ad/j/CalqsLin") :
java.lang.NoClassDefFoundError: C:/ad/j/CalqsLin
i haven't used rjava yet, I think I installed it on linux
for testing but no real usage, but this message
appears to come from jvm probably because you
specified an aboslute path. You can try this from
command line,

$ ls ../geo/dayte*
../geo/dayte.class

mmarchywka at phlulap01 /cygdrive/c/d/phluant/duphus
$ java ../geo/dayte
Exception in thread "main" java.lang.NoClassDefFoundError: ///geo/dayte
Caused by: java.lang.ClassNotFoundException: ...geo.dayte
        at java.net.URLClassLoader$1.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
Could not find the main class: ../geo/dayte.  Program will exit.

you want to search for the classpath and set that up then
refernce the class name not the path ( the class loader will follow
the path looking for it ).
Not sure how you do that in rjava under 'dohs but
if you search for that term is should be apparent.
And of course 'dohs and pdf aren't always friendly
for automated work so get something like cygwin and
reduce pdf's to text etc.

It appears that by default the current directory is on the
classpath. I must have installed this on 'dohs before
and if I copy the class file into R directory it
can find it,
library("rJava")
.jinit()
.jnew("foo")
Error in .jnew("foo") : java.lang.NoClassDefFoundError: foo
.jnew("dayte")
[1] "Java-Object{dayte at 1de3f2d}"

that's unlikely to fix all your problems, you want to set the classpath
but if you know the term and can load cygwin you should be able
to find the way to set that up.

So I got this error which means I don't understand very much.
I go to C:/ad/j and get
C:\ad\j>dir CalqsLin.class
Volume in drive C has no label.
Volume Serial Number is 9A35-67A2
Directory of C:\ad\j
04/23/2011 07:11 AM 14,651 CalqsLin.class
1 File(s) 14,651 bytes
0 Dir(s) 104,257,716,224 bytes free

Just to show my intentions,
I had next wanted to call this java function method:
linTimOfCalqsStgIsLev("201104052359599999",-4) using:
dblTim <-
.jcall(qsLin,"D","linTimOfCalqsStgIsLev","201104052359599999","-4")
but that will probably also be wrong?
Obviously I don't understand.

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Using Java methods in R

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