Develop Reference

IKVM.NET & Excel VBA

I'm using IKVM.NET in order to convert a Java library (signally, Strata) into a .NET library. Here are the steps I perform:
I download the latest Strata release.
I unzip all the JAR files contained into the lib folder of the archive to C:\Strata\, including the following auxiliary libraries:
commons-math3-3.6.1.jar
guava-26.0-jre.jar
joda-beans-2.4.0.jar
joda-convert-2.2.0.jar
slf4j-api-1.7.25.jar
I generate a keyfile for the library I want to create using the command sn -k "C:\Strata\Strata.snk".
Using the binary bytecode compiler of IKVM.NET, I convert the JAR files of Strata into a .NET library with the following command: ikvmc -out:"C:\Strata\Strata.dll" -keyfile:"C:\Strata\Strata.snk" -assembly:Strata -version:2.2.0 -fileversion:2.2.0 -target:library -platform:anycpu -recurse:"C:\Strata\*.jar".
Once the process described above is done, even if a few warnings concerning missing classes are shown, I obtain a working .NET wrapper of Strata. If I create a new Visual Studio project referencing the Strata.dll assembly, I'm capable of using its classes and methods without problems.
What I would really love to achieve is to make the wrapper work in Excel VBA macros, so that I can instantiate and use Strata classes in the subs, according to the contents of the sheets.
This is what I tried so far, but to no avail:
I register all the IKVM.NET libraries and the Strata wrapper into the GAC as follows: gacutil /i "C:\IKVM\IKVM.*.dll", gacutil /i "C:\Strata\Strata.dll".
I register the Strata wrapper as COM component and I create its types library as follows: regasm /codebase /tlb "C:\Strata\Strata.dll".
Now, when I open Excel and I go under Development > Visual Basic > Tools > References... I can see the TLB file of Strata (located at "C:\Strata\Strata.tlb") and I can add it to the current project. But as soon as I type something the window or I open the Objects Browser, Excel crashes without providing any meaningful information about what's going on.
I'm totally clueless about this issue.
Is my registration process correct? Do I have to register the IKVM.NET libraries too and create their type libraries? Should I include them into the Excel VBA project together with the Strata wrapper type libraries? Could the problem be caused by the fact that I'm using a x64 version of Excel and the wrapper has been compiled under AnyCPU? Do I need to edit the wrapper by adding a ComVisible attribute on every public class? May this problem be due to the fact that the wrapper contains weird method names like “\_Build01_\p”?

Rather than use IKVM.NET you can use Java directly to build an Excel add-in.
To build an Excel add-in in Java instead of having to use .NET, see https://exceljava.com.
There is even a Strata-Excel project that you might be interested in that wraps the Strata library in an Excel add-in: https://github.com/exceljava/strata-excel
I think you should find this much more convenient than converting the Java libraries to .NET.

Difference between a jar file and a library in Java

NetBeans allows the programmer to add a library and a jar file.
What is the difference between a jar file and a library? Is library similar to GAC assembly as in Windows.
There are similar questions, but they are way too specific and I was not able to understand the difference.

to put things very simple : library is a collection of jars
You could like create a global library java-ee which contains all Java EE related jar files. Then you could use this global library in your different projects. It will be simpler to manage them; and adding in new projects.

A JAR serves the same function an an Assembly in the C#/.net world. It's a collection of java classes, a manifest, and optionally other resources, such as properties files.
A library is a more abstract concept, in java, a library is usually packaged as a JAR (Java ARchive), or a collection of JARs.

A jar file is zip archive containing among other files, the java class files. A Netbeans library contains resources required by the project, including jar files.

If well understood: A library is simply a folder that groups classes. For example in JDK, a library present there is a group of classes stored together.
If not mistaken a .jar file is a group of compiled classes in .class format and was created by Java creators so a program will be OS independent; which means within a JVM you will run your app in .jar format on a Linux, Windows, etc without re-coding tour app for various OSs.

This article explains it all..
It states
Java's libraries are commonly known as class libraries. However, Java
refers to class libraries as packages.

Do Java programs natively support the concept of version?

I was wondering if there is any standard procedure to set a Java project's version (a bit like a Windows executable file version).
I'd like to have my application's code able to have introspection capabilities so it can know its own version.
Is it possible, at all, to do this with Java without resorting to have a .txt file in the directory with the version as contents?
If yes, the ideal would be to have Eclipse update the version each time it is compiled. Is this possible?

The Java native way to store version information is in the manifest files (this part of the tutorial is about version information).
You can use the Package class and its methods such as getImplementationVersion to get at those details at runtime.

I'm not sure how to tell Eclipse that I want it to create a .txt file in a given place each time it automatically builds a .java file, though..
Can I suggest that you take a look at Maven, and the release process that it supports.

Converting a Scala library to a DLL (.NET)

I'm trying to create a Dll out of a scala-class. I'm using IntelliJ together with SBT. I've already found a way to convert .jar files into a Dll, using the ikvm-converter. Now the problem: When I use "package" under SBT to create a .jar file out of my .scala file and try to convert it afterwards with ikvmc into a Dll the resulting library is empty when integrated in C#...
For example converting the Jama-Library (which is written in Java) works fine, where converting Scama (written in Scala) does not work.
Is there a way to do this conversion of scala code into a dll? Is there a "Scala to Java"-conversion tool?
Best Regards,
Christoph

I have no knowledge of .NET, but judging from SK-logic's and your comments to the questions: sbt package does not include the Scala runtime library, because it assumes you are going to export your project as a library to be used within other Scala projects.
Therefore, you will need to create a "fat" jar that contains the runtime. For example, in this blog you can see how the author creates a fully self-contained executable, by converting both the project jar and the runtime jar.
There are different tools to do that with sbt. The easiest would be sbt-assembly, but you will end up with a very large file, because it just adds the whole runtime. If that is a problem, you may want to filter the runtime instead, using the proguard plugin. More on this topic in another StackOverflow entry.

How do I build a single bundled JAR with all the needed classes to run a Java application?

I'm going to deploy a Java application with a custom launcher, and I need to have all the classes needed for my app in a single jar file so I don't have to deploy the entire Java SE libraries with it.
I was thinking of using some pre-existent ant tasks to create a target that recursively searches all my compiled classes files for its dependencies. After all the dependencies have been determined it would extract the needed class files from their JAR's, copy it along with my classes to an output directory and make a single jar from it.
If there's no such thing avaliable out of box, I can create one myself, but I need to know how references to other classes are stored in .class files. It could be much easier if there's some kind of java library like .NET's Mono.Cecil/System.Reflection that exposes an high level API for inspecting/manipulating Java.
Since I'm new to Java, I'm having some trouble in finding what is needed to acomplish those things. Can someone give me some direction?

Unfortunately, you cannot ship only part of Java SE - that will breach the license agreement. If you use Java SE, then all of Java SE must be available.
The simplest way to achieve this is to use an Ahead Of Time compiler. These take care of packaging only the classes you need, and adhere to the JDK license agreement by making the "unused" parts of the JDK available via optional download.
For example, Excelsior JET is a good AOT compiler and will package just the classes you need. It's not free for commercial use, although open source projects can apply for a free license grant.
Alternatively, you may simply assume that the user has the JRE already since it's installed on over 90% of desktops, and in cases where the JRE is not available, have your installer download one for the user. AdvancedInstaller has a free edition that will accomplish this.

After all the dependencies have been
determined it would extract the needed
class files from their JAR's, copy it
along with my classes to an output
directory and make a single jar from
it.
As an easy solution, if you use Eclipse IDE you use the following solution:
Under the Java project properties (right click):
Export... => Export as Runnable JAR
The exported JAR will have all its dependencies packed into it.
alt text http://www.ubuntu-pics.de/bild/97131/selection_016_mg6IDm.png

Here is one suggestion I found on the web:
<jar destfile="${build-abc}/abc.jar" duplicate="fail" index="true">
<zipfileset src="${compile-lib}/demo.jar" includes="**/*.class"/>
</jar>
This should add the dependencies to the jar (as shown with demo.jar). You still have to adapt the manifest file so that the added jars appear on the classpath.
This doesn't solve the 'Java SE' classes problem - you'll have to bundle a jre in the installer package or depend on an existing one on the target system.

You won't have to deply Java SE classes, as they already are in the customer JRE.
If your dependencies are expressed ion a common way (through Maven or Ivy) i guess it's quite easy to find an equivalent of maven uberjar task ... which will do what you want to do, but in a more simple way (as it simply repacks all jars in one big jar).