`SWIG/Examples/java/simple/`

## Simple Java Example

`$Header: /cvsroot/swig/SWIG/Examples/java/simple/index.html,v 1.4 2004/11/02 22:13:36 wsfulton Exp $`

This example illustrates how you can hook Java to a very simple C program containing a function and a global variable.

## The C Code

Suppose you have the following C code:

>     /* File : example.c */

>     /* A global variable */
>     double Foo = 3.0;

>     /* Compute the greatest common divisor of positive integers */
>     int gcd(int x, int y) {
>       int g;
>       g = y;
>       while (x > 0) {
>         g = x;
>         x = y % x;
>         y = g;
>       }
>       return g;
>     }

## The SWIG interface

Here is a simple SWIG interface file:

>     /* File: example.i */
>     %module example

>     extern int gcd(int x, int y);
>     extern double Foo;

## Compilation

1. `swig -java example.i`

2. Compile `example_wrap.c` and `example.c` to create the extension `libexample.so (unix)`.

## Using the extension

Click here to see a program that calls our C functions from Java.

Compile the java files `example.java` and `main.java` to create the class files example.class and main.class before running main in the JVM. Ensure that the libexample.so file is in your LD_LIBRARY_PATH before running. For example:

>     export LD_LIBRARY_PATH=. #ksh
>     javac *.java
>     java main

## Key points

- Use the `loadLibrary` statement from java to load and access the generated java classes. For example:

  >     System.loadLibrary("example");

- C functions work just like Java functions. For example:

  >     int g = example.gcd(42,105);

- C global variables are accessed through get and set functions in the module class. For example:

  >     double a = example.get_Foo();
  >     example.set_Foo(20.0);