Developing and using Qt based applications written in Java ========================================================== This document explains how to develop and use Qt based programs written in Java. This is what the Qt java bindings from the package libqt3-java are designed to accomplish. Firstly, the bindings should work with any java compiler and VM properly implementing the JNI interface, but they have only been tested with the GCJ compiler and GIJ interpreter from the GCC suite. Note that the bindings are not compiled to native code, using GCJ's unique capability to do this, they are simply compiled to .class files, and interpreted, in the classical Java manner. Secondly, when compiling and running apps using the Qt Java bindings, you need to add "/usr/share/java/qtjava.jar" to the CLASSPATH. E.g. export CLASSPATH="/usr/share/java/qtjava.jar:/usr/share/java:." javac Whatever.java java Whatever And, that's basically the hard part of it all. For the rest, developing Qt Java apps is much like Qt C++ apps, except that working with slots is easier, and compiles may be faster as well. The API should be completely similar to the Qt C++ API, so the standard Qt docs should translate pretty easily. There are a lot of Qt Java usage examples in /usr/share/doc/libqt3-java/examples. If you're interested in developing TDE applications using Java, look at the libtrinity-java package. Generating native executables ----------------------------- It is also possible to produce native executables with the following gcj invocation: export CLASSPATH="/usr/share/java/qtjava.jar:/usr/share/java:." gcj -fjni Somefile.java /usr/share/java/qtjava.jar --main=Somefile LD_LIBRARY_PATH=/usr/lib/jni ./a.out As this will compile the full qtjava.jar into native code, the resulting executable will be rather large. If you plan on having several of these executables, it may be worth creating a shared qtjava library, like this: gcj -fjni -shared /usr/share/java/qtjava.jar -o libtqtjava-shared.so And then, after you put libtqtjava-shared.so in /usr/lib or similar, you can go like: gcj -fjni Somefile.java --main=Somefile -lqtjava-shared LD_LIBRARY_PATH=/usr/lib/jni ./a.out In the future, I'll investigate the possibility of shipping the qtjava-shared library in the Debian packages. Also, in order to avoid the necessity of setting the LD_LIBRARY_PATH environment variable, the option -Djava.library.path=/usr/lib/jni can be passed to the gcj invocation. There is, however, a bug [1] in gcj that prevents this from working, and it's only fixed in gcj-4.0. [1] http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18234