Using Java as a Graphical User Interface for C Library Routines

Introduction

Java is a very nice language to write high level code. It is well-documented, portable across platforms, and supported with a huge array of support classes. By using Java for a program's Graphical User Interface to call functions in libftdi and libusb, we get the convenience of Java with the speed and proven operation of those C libraries.

Sun Microsystems, the creator of Java, has described how to interface Java code to C code in an online book The Java Native Interface Programmer's Guide and Specification. Chapter 2 of that book is the basis for the HelloWorld.java example that follows. Minor modifications of their compilation procedure, however, were needed for Linux on my system:

Demonstration of C code linkage from Java - HelloWorld.java

1. Create a Java program called "HelloWorld.java" that contains the following lines:

   class HelloWorld {
   	private native void print();
   	public static void main(String[] args) {
   		new HelloWorld().print();
   	}
   	static {
   		System.loadLibrary("HelloWorld");
   	}
   }
   

2. Compile HelloWorld.java:

   javac HelloWorld.java
   		

3. Create a C header using Sun's javah tool:

   javah -jni HelloWorld
   		

4. Create a sample C shared library source code called "HelloWorld.c":

   #include <jni.h>
   #include <stdio.h>
   #include "HelloWorld.h"
   
   JNIEXPORT void JNICALL Java_HelloWorld_print(JNIEnv *env, jobject obj)
   {
   	printf("Hello World from C to Java!\n");
   	return;
   }
   int main(int argc, char** argv){return 0;};
   		

5. Compile the shared library code:

   cc -shared -fpic -I/usr/java/jdk1.5.0_09/include -I/usr/java/jdk1.5.0_09/include/linux HelloWorld.c -o libHelloWorld.so
   		

6. Run the code:

   java -Djava.library.path=. HelloWorld
   		

7. The output should be:

   Hello World from C to Java!
   		

Java version of ftdi_eeprom_main.c

Under Construction

Java version of libftdi_example_bitbang2232.c

Under Construction

Last updated: January 9, 2007