Running native code in Java

Uses JNI to call a library that implements code that runs on the native platform.

Based on http://mrjoelkemp.com/2012/01/getting-started-with-jni-and-c-on-osx-lion/.

The above example starts with the Java class that contains a method declared to be a native interface to the platform. The example then uses a Java command line tool to generate a C++ header that declares the method signature that needs to be implemented in C++. The C++ code was then added followed by compiling and linking the code to create the .jnilib.

Prerequisites

• JDK is installed
• GNU g++ is installed. This was already the case since I was developing on a Mac.

Building the Simplified Project

$ ./build.sh

Running the Simplified Project

$ java HelloWorld

should print the following to standard out: Oh JNI, how cumbersome you are!

Getting it to work by compiling from cygwin for Windows

It required changes to the build.sh script so created a new build script for Windows.

Used the following tutorial to help: https://www3.ntu.edu.sg/home/ehchua/programming/java/JavaNativeInterface.html

To build (from cygwin command prompt):

1. invoke ./buildForWin.sh

To run (from Windows command prompt -- NOT cygwin):

1. copy cygwin1.dll to this folder
2. invoke: java -cp .\ -Djava.library.path=.\ HelloWorld