Develop Reference

How to make VS Code recognize .class file?

I'm trying to use VS Code with java, but I have an issue.
As a student, my teacher gives me a file named Clavier.class.
I have already wrote a programm with another IDE, and when I execute it in the command of Windows, it works without any problem. But, when I put this programm in VS Code, it doesn't recognize Clavier.saisirInt, which is a static method in Clavier.class. I guess that VS Code can't use a class which is in a File.class, but is there a way to make it works ?
Here is an image of my workspace and you can see the error at the bottom

I assume your lib/ folder is placed onto the execution classpath. If this is the case, that's where compiled class files should go, not next to your sources
Otherwise, you'll need to inspect the java command that actually runs your code to see what/if the -cp argument is set to, or include those class files similar to how the documentation shows for JAR files (which are just zipped packages of class files, and honestly what the teacher should provide instead)
By default, VS Code will reference all JAR files in workspace's lib directory using the glob pattern lib/**/*.jar
And so, you need to adjust this to include lib/*.class after moving your files there

Convert .java files to single .jar

I read and searched almost everywhere, yet i have no answer.
I have a project with multiple .java files, and i need to export them as a single .jar file.
One of the main questions is based on the fact that i don't have a main class.
What can i do to go through that ? Shall i create a main but never run it? Or there's any way around?
Offtopic ( might be usefull): i want to do this in order to use the jar file in IKVM
Thank you!

You do not need a main method to create a jar. There are many such jars out there such as utilities packages. They don't contain any code that would make sense to execute on it's own since it only contains code that makes your application easier to write.
First compile your code using Netbeans or command line javac utility. This will give you .class files.
Now for creating the jar... You can simply create the jar (which is basically a glorified zip archive) by using the command-line jar tool.
jar -cvf my archive.jar myprogram/
Make sure that the file path within the jar archive match the package name of the classes. It is not uncommon to accidentally get an extra layer of directories.
You probably should have searched stackoverflow first since how-to-create-a-jar-file-in-netbeans seems to cover exactly what you're looking for.

Do you want to use the jar as a external library or a program itself?
If it will be a external library, you don't need a main class. In eclipse you can export as a jar file (select classes-> right click-> export as jar).
If it will be a program itself, then you need a main class.

You really need to create main class file, write code in function main(String args[]) which use your java classes and compile it by javac.

Using .class files in netbeans

I'm trying to use a .class file I downloaded for a uni project. I don't have the .java file to go with it. I am using netbeans.
I tried just adding it to the project src folder
I tried using "add JAR/folder" on libraries and adding the directory containing it
I also tried creating a JAR file of the directory containing it and adding that
Greatly appreciate any suggestions

You should do two things:
Create a jar of the class file you received
Create an overview which methods the classfile offers
For the latter you have at least two options. One is to use a decompiler (some authors of APIs deny you to use this) like JD-GUI. The second options is to use javap, which comes with your JDK (I link to Java 8, but it exists in prior versions too). Simply call javap yourfile.class and you will see which method signatures the class offers.
But the easiest way to see the classes / methods inside the .class file is JD-GUI, so if you are not running into any legal issues use that approach.

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.

Java: How to Integrate Other Software

I've always been impressed by the StackOverflow hive mind, and was hoping you could point me in the right direction here.
I've taken some courses in Java programming, and understand how to write a fairly complex Java program. However, I've never learned how to integrate others' software into my own programs.
For a new project, I'd like to integrate a part-pf-speech tagger and chunker into my code, but have no idea how to "load" these programs (if load is the correct term).
I'm certainly not looking for step-by-step instructions, but rather a guide for how to go about this sort of issue. If anyone could get me started in the right direction, I would greatly appreciate it.
Thanks,
Adam

It looks like the externals you want to use are themselves in Java. This means you're in luck - you can use pure java language features to make it work.
There are two things to it:
1) your source files that interact directly with the external libraries have to be imported, or otherwise you'll have to refer to them using the fully qualified classname.
Importing is done with the import statement. These statements should appear right before your class declaration, like so:
import foo.*; //import all classes from the package foo
import foo.bar.Baz; //import only the Baz class from the package foo.bar
public class MyClass {
Baz myBaz = null; //declare a member of type Baz class from package foo.bar
foo.bar.BazBaz myBazBaz = null; //by using a fully qualified classname, I didn't need to write an import statement for foo.bar.BazBaz
}
2) when you compile your sources, the java compiler needs to know where to look for classes you referenced in your source. This is done via the classpath.
The classpath can be a list of just .class files (compiled java classes), but also .jar files (java archives) and .zip files. Typically a project will package all classes it needs in one or more .jar files.
The location of these classes have no bearing on the way you interact with them in java code. It's the compiler's job to read these jars and class files and locate the classes you referred to in your code. If the compiler can't locate the classes you're referring to, you will get a compile time error and you can't compile your program.
You can specify the classpath as an argument to the java compiler command line (http://docs.oracle.com/javase/6/docs/technotes/tools/windows/javac.html#options). However, this becomes unwieldy very rapidly.
Instead, you should use a build tool like ant to do this work for you. The best way to get started is to read this page: http://ant.apache.org/manual/index.html.
From there, go to "Using apache ant" and then to "Writing a simple build file" in its entirety, they explain how to set up the classpath very well there.

You'll need their classes on your classpath when compiling, and again when running your program.
It appears that those projects distribute both src and jars. Grab the jars, and make them available on your classpath. Once your classpath is set up you'll need to import any specific classes/packages that you're using.
See this tutorial on managing the classpath. It covers the basics for command-line compilation/execution; if you're using a particular build system or IDE then the instructions will vary.
Also note the specific instructions at the second link for making data files available. For this they're also using the classpath.

Configure your build path to include the .jar files.
If you're using Eclipse, you would right click on the project file in the Project Explorer, then select Configure Build Path. Finally, add external archive (the ones you've downloaded). Now those functions will be readily available in your program.
Or a more robust way is to create a folder called "lib" in your eclipse project and include all jar files in there. Then from the Configure Build Path window you select those jar files in the lib folder. This makes it easy to share projects with other programmers regardless if they are on Windows or Linux (when adding external jar it saves the absolute path so if something on C:\ will not be found on someone else's PC) Also provides nice integration of dependency libraries on source code managers like GIT, CVS and SVN.

Well typically Java libraries are distributed as a JAR file. Then in your program, you can simply import the new packages and use the provided API.
When you compile and run, you have to make sure that the libraries are included in your class path so they know where to look for the packages.