Java Native Methods Interface

Another feature of Java is that C and C++ functions can be used by using java native interface.

In this project, a C version of the arithmetic functions are implemented and are used both in client and server side.
I will briefly explain how native functions are implemented in this project.

1. First a Java object that have native functions calls is created This would be: native/Arithmetic.java Basically, if we look at this code:

        static {
                System.loadLibrary("Arithmetic");
        }
        // calls for native C functions
        public native int Add(int a, int b);
	.......

A Java method loadLibrary() is used to load the library Arithmetic which is going to be implemented. This library must have the functions which are defined as public native

Then, it is compiled by using

	% javac Arithmetic.java

After that, we need to create the header files for the C program. This is done by using:

	% javah -jni Aritmetic

This header holds the function declarations: native/Arithmetic.h (In order to access this file the system must be built!:)

Then, we created the C file:native/Arithmetic.c. You should include Arithmetic.h file and jni.h which is located in the Java include directory. When using function calls, you should be careful about Java's naming conventions.

Then we compiled the C code to create a .so, shared object file.(If you are in a Windows system, you should create a DLL). The shared object is created like this:

     % cc -G Arithmetic.c -I/afs/bp.ncsu.edu/contrib/jdk117/java/include \
       -I/afs/bp.ncsu.edu/contrib/jdk117/java/include/solaris -o libArithmetic.so

The pathnames are specific to the environment that we used. If you use a different environment, change pathnames accordingly.

Now you can use Arithmetic.class and libArithmetic.so files to call native functions!

For more information about JNI, these links can be checked out: