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3<title>SWIG:Examples:java:simple</title>
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9<tt>SWIG/Examples/java/simple/</tt>
10<hr>
11
12<H2>Simple Java Example</H2>
13
14<p>
15This example illustrates how you can hook Java to a very simple C program containing
16a function and a global variable.
17
18<h2>The C Code</h2>
19
20Suppose you have the following C code:
21
22<blockquote>
23<pre>
24/* File : example.c */
25
26/* A global variable */
27double Foo = 3.0;
28
29/* Compute the greatest common divisor of positive integers */
30int gcd(int x, int y) {
31 int g;
32 g = y;
33 while (x > 0) {
34 g = x;
35 x = y % x;
36 y = g;
37 }
38 return g;
39}
40</pre>
41</blockquote>
42
43<h2>The SWIG interface</h2>
44
45Here is a simple SWIG interface file:
46
47<blockquote>
48<pre>
49/* File: example.i */
50%module example
51
52extern int gcd(int x, int y);
53extern double Foo;
54</pre>
55</blockquote>
56
57<h2>Compilation</h2>
58
59<ol>
60<li><tt>swig -java <a href="example.i">example.i</a></tt>
61<p>
62<li>Compile <tt><a href="example_wrap.c">example_wrap.c</a></tt> and <tt><a href="example.c">example.c</a></tt>
63to create the extension <tt>libexample.so (unix)</tt>.
64</ol>
65
66<h2>Using the extension</h2>
67
68Click <a href="main.java">here</a> to see a program that calls our C functions from Java.
69<p>
70Compile the java files <tt><a href="example.java">example.java</a></tt> and <tt><a href="main.java">main.java</a></tt>
71to 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:
72<blockquote>
73<pre>
74export LD_LIBRARY_PATH=. #ksh
75javac *.java
76java main
77</pre>
78</blockquote>
79
80<h2>Key points</h2>
81
82<ul>
83<li>Use the <tt>loadLibrary</tt> statement from java to load and access the generated java classes. For example:
84<blockquote>
85<pre>
86System.loadLibrary("example");
87</pre>
88</blockquote>
89
90<li>C functions work just like Java functions. For example:
91<blockquote>
92<pre>
93int g = example.gcd(42,105);
94</pre>
95</blockquote>
96
97<li>C global variables are accessed through get and set functions in the module class. For example:
98<blockquote>
99<pre>
100double a = example.get_Foo();
101example.set_Foo(20.0);
102</pre>
103</blockquote>
104</ul>
105
106<hr>
107</body>
108</html>