How do I integrate my Java program into a project written in C#?

Question

I've heard that Reddit and Facebook have written certain parts of their applications in C/C++ to speed up run times. However, to my knowledge, the main platforms are written in other languages. How do they get these programs to work together?

I recently wrote a program in Java to allow me to push/pull data from a RESTful resource. A colleague now requested that I implement into his. Unfortunately, his application is authored in C#.net and I don't know C#, nor do I want to re-write my code. Is it possible to simply create some kind of wrapper/shim to integrate the two systems together, i.e. the main C# program requests some kind of data file/object from my Java program?

Also, would it just be more reasonable to simply learn how to re-write the program in C#?

Answer 1

C# and Java are not so different in a lot of ways, so porting your app would probably not be a huge undertaking (depending on various factors, of course.). As they are both managed languages, I wouldn't expect to see a performance gain when calling C# code instead of native Java.

However, you may find this link useful: http://codefry.blogspot.co.uk/2012/01/calling-net-dlls-from-java-code-without.html?m=1#!/2012/01/calling-net-dlls-from-java-code-without.html

Answer 2

C# and Java are both hybrids of interpreted and compiled languages. Java is compiled to Java bytecode, and the JVM runtime interprets it into native instructions. C# is compiled in MSIL (Microsoft Intermediate Language), and the .NET runtime interprets the MSIL into native instructions. Both C# and Java have means of interacting directly with native binaries. Java has the Java Native Interface (JNI), and while .NET doesn't have a particular name for it, .NET applications can interact with native assemblies as well. Since C and C++ compile to native assemblies, it's possible to interface Java or .NET code with the binaries generated from C and C++ code.

When you hear about an interpreted language using a native binary, it's usually for one of two reasons, in my experience. The first is because what the native binary does is complex enough that the interpreter's inefficiencies actually make a large difference in performance. Less performance critical code can still be written in interpreted languages without noticeable impacts on overall performance, and the things the interpreted language gives you speed up development and improve quality. (For example, most interpreted languages do memory management automatically.) The other reason is reuse. Many tools (such as database drivers) are provided in native format; providing a wrapper around the native binaries is a simpler, cheaper (and probably more reliable) option than trying to re implement all that code in the interpreted language. Most interpreted languages provide a native interface because these practices are so widely used.

There is no officially supported means of interfacing .NET and Java code. They are both interpreted languages, and it's rare to find languages interfacing with any kind of library besides native.

Whether it's "too hard" to learn C# is an entirely subjective question and heavily dependent on your current knowledge and experience as well as the scope of the other application and the timeline. As such, we can't answer that for you.

Answer 3

There is actually an excellent open source project for using Java bytecode from .NET languages. It's called IKVM. You can either dynamically interpret Java .class files on the fly, or you can first "compile" the Java bytecode to .NET bytecode to produce a .NET assembly and then use that along with some IKVM DLL's. I've used the pre-compiling option successfully to incorporate a large Java computational geometry library (JTS) into a C# application.