# Tuesday, January 4, 2005
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Using IKVM as a JRE with Eclipse

A while ago Howard Gilbert wrote instructions on how to use IKVM as the target runtime with Eclipse (i.e. not running Eclipse in IKVM, but running the code you develop with Eclipse in IKVM).

My apologies to him for not posting this earlier (and for not adding it to www.ikvm.net, where it really belongs).

I could not find instructions in the documentation about using vanilla
Eclipse (under Java) to develop code that you then run (in Eclipse) under
IKVM. The trick is to define IKVM to Eclipse as an additional Java Runtime
Environment. It seems that this might be useful to post somewhere:

[This uses Windows and an installed Microsoft .NET Framework, but it can
probably be adapted.]

Eclipse runs under the default version of Java installed on your machine
(type "java -version" to find out). However, it can be configured with the
directories of other Java Runtime Environments (JRE's). In the Run . panel,
you can select a particular JRE in which to run each application.

Eclipse believes that a directory is a JRE if it has two things. 
1. It must have a {jre}/bin/java.exe file. 
2. It must have a {jre}/lib/rt.jar file.

Start with a binary distribution of IKVM in c:\ikvm. Copy
c:\ikvm\bin\ikvm.exe c:\ikvm\bin\java.exe. Create a c:\ikvm\lib and copy
into it the rt.jar from your favorite real Java runtime. Don't worry
because, of course, it will not really be used.
[Jeroen: You can also run ikvmstub on IKVM.GNU.Classpath.dll and rename the
resulting IKVM.GNU.Classpath.jar to rt.jar]

In Eclipse, pull down the Window menu option and select Preferences - Java -
Installed JRE's. Click the Add... button. Leave the type as "Standard VM". A
suggested "JRE name" is "IKVM". Point the "JRE home directory" to c:\ikvm.

The JRE system libraries box fills up with the libraries found in the
{jre}/lib directory. For the moment, the only such library is rt.jar.

Now build a simple Java program. When you want to run it, select Run - Run
... In the JRE tab, click the "Alternate JRE" option and select IKVM from
the pulldown. If you want to be clear, in the "Java executable" select
Alternate and type in "ikvm" (that is the ikvm.exe program). 

Now run the program. It ran under IKVM, but it is indistinguishable from

Now run ikvmstub on your favorite version of mscorlib.dll and put the
resulting jar file in c:\ikvm\lib\mscorlib.jar. After that, you should be
able to ikvmc your favorite JAR files, then put the jar file into /lib and
the generated dll into /bin. This is just a suggested use of the library

Sanity check: The Eclipse Package Explorer displays the JAR files as Eclipse
sees them during compilation. Even if you intend to run the program under
IKVM, Eclipse is going to compile them with your default real Java and its
libraries. So when you add JAR files to c:\ikvm\lib this doesn't put them in
the compiler path. You have to manually add the extra JAR files to your
project, and then the compiler knows to use them as the source is compiled.
At runtime the DLLs will either be automatically located because they are in
the same directory with ikvm.exe. 

So use Project - Properties - Java Build Path - Libraries - Add External
Jars to add mscorlib.jar to your project, and write a small Java program
using some CLI classes. Note that all the usual Eclipse IDE features work.
Type "cli.System.Console." and pause. Eclipse likes (default behavior of a
configurable feature) to convert explicit class names to imports, so it will
add a

import cli.System.Console

to the import group, replace what you have just typed with "Console." and
then display a popup with the list of methods of the System.Console class to
complete the expression.

When it doubt, in the Explorer panel on the left expand any of the jar files
(such as mscorlib.jar) to see the actual fully qualified names of the
classes generated by ikvmc.

Save the file and it gets compiled.

Run it (assuming again you set Run ... to use the IKVM "JRE") and you get
the expected output. Now there is no question that you are running IKVM
because you are calling CLI libraries.
Tuesday, January 4, 2005 9:09:48 AM (W. Europe Standard Time, UTC+01:00)  #    Comments [0]