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  <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 &gt; 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="runme.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="runme.java">runme.java</a></tt>
  to create the class files example.class and runme.class before running runme 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 runme
  </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>
  
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