Minimal example of using SWIG with Java and CMake

Build:

mkdir build
cd build
cmake ..
cmake --build .

Run:

java -Djava.library.path=. -jar Main.jar

Output:

124

Troubleshooting:

On Windows, if your Java installation is 64-bit then make sure to use a 64-bit C++ compiler.
e.g. if you are using Visual Studio 2015: cmake -G "Visual Studio 14 2015 Win64" ..
To detect the Java version, use java -version and javac -version
You should set your JAVA_HOME variable to avoid problems such as CMake not able to find JNI.
e.g. on Ubuntu 14.04 with OpenJDK: export JAVA_HOME=/usr/lib/jvm/java-7-openjdk-amd64/
Check that java -version, javac -version and JAVA_HOME all refer to the same version.
(on Windows: echo %JAVA_HOME%)

Tested on:

Windows (10) with Visual Studio 2015, 2013 and Oracle JDK.
Linux (Ubuntu 15.10, 14.04; Debian 7, 8) with gcc and OpenJDK or Oracle JDK.
MacOSX (10.11) with clang and Oracle JDK.