Calling Java from Fortran using JNI

[Chaitra_R_]

Hello,

I have a program to call Fortran from Java. The codes for func.f95, addC.c, and addJava.java are as follows:

FUNCTION  add(c, iflag) RESULT(f)
INTEGER, INTENT(IN):: c
INTEGER, INTENT(OUT):: iflag
INTEGER:: f
INTEGER:: i

i=10
f=c+i

PRINT *, f  
PRINT *, iflag
END FUNCTION

#include <stdio.h>
#include "addJava.h"  

extern int add(int *, int *);

JNIEXPORT jint JNICALL Java_addJava_add(JNIEnv *env,
                       jobject obj, jint c, jint iflag) {

    int result;

    printf("-- We are now in the C program CCode --\n");
    printf("c=%d, iflag=%d\n",c,iflag);

    printf("Call the FORTRAN code\n");
    result = add(&c,&iflag);

    printf("-- We have now returned back to the C program --\n");
    printf("c=%d, iflag=%d\n",c,iflag);

    printf("Result = %d\n",result);
    return result;
}

import java.io.*;
import java.lang.*;
import com.sun.jna.Library;
import com.sun.jna.Native;
import com.sun.jna.Platform;
import com.sun.jna.ptr.IntByReference;


class addJava {

    private native int add(int element, int iflag);

    public static void main(String args[]) {
	Native.setProtected(true);

	System.out.println(System.getProperty("jna.library.path"));
	System.out.println(System.getProperty("java.library.path"));
	System.load("/home/chaitra/Research/JAVA/examples/JNI/add/add.so");

        System.out.println("-- We are in the Java program JavaCode --");
        addJava result = new addJava();

        System.out.println("Call the C code");
        int sum = result.add(10, 0);

        System.out.println("-- We are back in Java --");
        System.out.println("Result = " + sum);
        System.out.println("Exit Java");
    }
}

I want to know how to call Java from Fortran i.e., Fortran -> C -> Java. I want to pass the value of variable c to a Java program that computes result=c+10 and returns the value to Fortran. How can this be done? Please help!

[pbkenned1]

I can't compile your C driver.  Can you please attach addJava.h?

Patrick

[pbkenned1]

Since I needed to modify the java code to reflex my system path, I just generated my own addJava.h, so there's no need to attach your version (I only wanted to see what your java compiler produced for the C header). 

I found the easiest way to do this exercise was simply to put the C driver and Fortran function in a shared object, and then make that available for java execution. 

Incidently, in the Fortran function, regarding 'INTEGER, INTENT(OUT):: iflag', iflag is modified, so I just made it INTENT(IN). 

Otherwise, the compiler complains:

[U544731]$ ifort -c add-orig.f90
add-orig.f90(1): warning #6843: A dummy argument with an explicit INTENT(OUT) declaration is not given an explicit value.   [IFLAG]
FUNCTION  add(c, iflag) RESULT(f)
-----------------^
[U544731]$

This now all seems to work fine, considering the above changes.

[U544731]$ export LD_LIBRARY_PATH=./:$LD_LIBRARY_PATH

[U544731]$java addJava

-- We are in the Java program JavaCode --
Call the C code
-- We are now in the C program CCode --
c=10, iflag=0
Call the FORTRAN code
          20
           0
-- We have now returned back to the C program --
c=10, iflag=0
Result = 20
-- We are back in Java --
Result = 20
Exit Java
[U544731]$

Hope this helps.

Patrick