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<html>
<head>
<title>SWIG:Examples:java:simple</title>
</head>
<body bgcolor="#ffffff">
<tt>SWIG/Examples/java/simple/</tt>
<hr>
<H2>Simple Java Example</H2>
<p>
This example illustrates how you can hook Java to a very simple C program containing
a function and a global variable.
<h2>The C Code</h2>
Suppose you have the following C code:
<blockquote>
<pre>
/* 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;
}
</pre>
</blockquote>
<h2>The SWIG interface</h2>
Here is a simple SWIG interface file:
<blockquote>
<pre>
/* File: example.i */
%module example
extern int gcd(int x, int y);
extern double Foo;
</pre>
</blockquote>
<h2>Compilation</h2>
<ol>
<li><tt>swig -java <a href="example.i">example.i</a></tt>
<p>
<li>Compile <tt><a href="example_wrap.c">example_wrap.c</a></tt> and <tt><a href="example.c">example.c</a></tt>
to create the extension <tt>libexample.so (unix)</tt>.
</ol>
<h2>Using the extension</h2>
Click <a href="main.java">here</a> to see a program that calls our C functions from Java.
<p>
Compile the java files <tt><a href="example.java">example.java</a></tt> and <tt><a href="main.java">main.java</a></tt>
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:
<blockquote>
<pre>
export LD_LIBRARY_PATH=. #ksh
javac *.java
java main
</pre>
</blockquote>
<h2>Key points</h2>
<ul>
<li>Use the <tt>loadLibrary</tt> statement from java to load and access the generated java classes. For example:
<blockquote>
<pre>
System.loadLibrary("example");
</pre>
</blockquote>
<li>C functions work just like Java functions. For example:
<blockquote>
<pre>
int g = example.gcd(42,105);
</pre>
</blockquote>
<li>C global variables are accessed through get and set functions in the module class. For example:
<blockquote>
<pre>
double a = example.get_Foo();
example.set_Foo(20.0);
</pre>
</blockquote>
</ul>
<hr>
</body>
</html>
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