Does a Java to C++ converter/tool exist?

I always asked myself if it would be possible to make a Java to C++ converter.

Maybe a tool that converts the Java syntax to the C++ syntax?

I am aware that the languages differ, but simple things like loops where the semantics match 1 to 1.

Is there such a tool? Or is it possible to make one?

It's possible to do anything given enough time, money and resources. Is it practical? Beyond trivial examples not really. Or rather it depends on what constitutes an acceptable error rate.

The real problem is that the idioms are different in Java to C++. Java to C# for example would actually be far easier (because the idioms are much more similar). The biggest of course is that C++ has destructors and manually managed memory. Java uses finally blocks for this kind of behaviour and has garbage collection.

Also Java has a common Object supertype. C++ doesn't.

The generics to templates would be nigh on impossible I would imagine.

The Firefox HTML5 parser is written in Java and converted to C++. But I think the converter used there is quite specific for this project. Interestingly, it turned out the resulting C++ parser was faster than the old parser written in C++.

I'm also writing a converter as part of the H2 database, under src/tools/org/h2/java. The idea is to allow converting a subset of the H2 database to C++, so this is also not a general purpose translater.

And there is the open source project J2C.

So there are ways to convert Java to C++. But don't expect the translator support all features, and don't expect the resulting code to be any faster than a good Java JVM.

Is is possible, no question, but it won't be so simple. It would be a Java compiler which generates C++.

If you want to do that from scratch, it will be very hard, you have to do all the work javac and the JVM do for you (e.g. garbage collection).

Btw. Google has a Java to JavaScript compiler (included in GWT)

There is one, bit I am not sure if it actually works. http://tangiblesoftwaresolutions.com/Product_Details/Java_to_CPlusPlus_Converter_Details.html">Java to C++ Converter-Tangible Software Soulutions.

It is weird how there are c++ to java converters, but only 1 java to c++ converter.

As said it would be tough to convert Java to C++ but we can have an applicaiton or tool that generates code in Java and equivalnet C++ code.

I know one applicaiton which generates code in C++/Java/C# given a model which has its own way to deifine it.

That tool belongs to CA and name is CA Plex. Search on www.ca.com

http://www.tangiblesoftwaresolutions.com/Order/Order_Upgrade_Instant_CPlus_Java_Edition.htm

Depends on the domain of where the code will be used, from a learning perspective perhaps it might be interesting.

i just found this via a google as I remembered seeing one in Univeristy that created code based on uml.

There are programs out there that claim they can do this, but none have gained enough popularity to be frequently mentioned, so we'll leave them at "attempts". Making a converter would require a lot of AI built into your program. The difficulty is increased tenfold when swing is involved because GTK/wxWidgets/Qt/win32 API all differ greatly from swing. But it is possible. Not that the code quality will be great, and no guarantees your program won't crash due to separate memory handling methods, but it's possible.

Something neat would be a tool , that translate java to "C++ using Java API" (like GNU GCJ CNI), one problem remain is to manage array.length (array not vector) ...

The main issue is that java is a language that is written and designed to talk to a VM. I suppose it would be possible, but all you would be left is a very poorly optimized application with a self translating layer doing what the VM already does. I mean, sure, it is possible, it still wouldn't be a solution for anything i could think of. If your looking to make your sluggish java app native, maybe your thinking too hard, just use an application like JET, its actually quite good, and will give you the benefits a native app would bring. Of course if the VM is already doing what the app is asking it to do just as well as native code could(it happens.. sometimes :P) it might change nothing.

Java to c#, tho, sounds more reasonable, as both the languages are written in similar ways, talking to a framework as such, but this would still leave code very much unoptimized as code written from scratch for a particular framework can not be bested.

Java to C would actually be the easiest. Remember you need to convert the language, If you do that, the required libraries can be converted by your new compiler. In other words Swing and AWT should not be a big problem...

I would start by taking a good look at the Java Native Interface (JNI). The JNI is a part of java which allows it to be used with C and C++. The reason I would start here is that it becomes fairly obvious how parts of Java may be implemented in C. Once I had a grasp on basic structures, like how Java Objects can be mapped onto C structures (struct) and how pretty much everything in Java is an Object including arrays, I might peek at the Open JDK source code.

The actual converter would have to convert all the imported Java libraries (and their imported libraries and so on...) which means you would need the source code for everything. This conversion no small task since the Java libraries are large.

The process would be time consuming, but no AI should be required. However, I see no reason to perform a conversion like this. It looses the portability of Java and would not gain the efficiency of C (except that it would be compiled to native code, but it would be better to compile the machine code directly from the Java).