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| author | Lorry Tar Creator <lorry-tar-importer@baserock.org> | 2009-08-18 20:56:02 +0000 |
|---|---|---|
| committer | Lorry <lorry@roadtrain.codethink.co.uk> | 2012-09-25 16:59:08 +0000 |
| commit | 9f8a09ed743cedd9547bf0661d518647966ab114 (patch) | |
| tree | 9c7803d3b27a8ec22e91792ac7f7932efa128b20 /Examples/java/class/index.html | |
| download | swig-tarball-master.tar.gz | |
Imported from /srv/lorry/lorry-area/swig-tarball/swig-1.3.40.tar.gz.HEADswig-1.3.40master
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diff --git a/Examples/java/class/index.html b/Examples/java/class/index.html new file mode 100644 index 0000000..cf9130c --- /dev/null +++ b/Examples/java/class/index.html @@ -0,0 +1,197 @@ +<html> +<head> +<title>SWIG:Examples:java:class</title> +</head> + +<body bgcolor="#ffffff"> + + +<tt>SWIG/Examples/java/class/</tt> +<hr> + +<H2>Wrapping a simple C++ class</H2> + +<p> +This example illustrates the high level form of C++ class wrapping performed +by SWIG. In this case, a C++ class has a proxy Java class, which +provides access to C++ class members. + +<h2>The C++ Code</h2> + +Suppose you have some C++ classes described by the following (and admittedly lame) +header file: + +<blockquote> +<pre> +/* File : example.h */ + +class Shape { +public: + Shape() { + nshapes++; + } + virtual ~Shape() { + nshapes--; + }; + double x, y; + void move(double dx, double dy); + virtual double area() = 0; + virtual double perimeter() = 0; + static int nshapes; +}; + +class Circle : public Shape { +private: + double radius; +public: + Circle(double r) : radius(r) { }; + virtual double area(); + virtual double perimeter(); +}; + +class Square : public Shape { +private: + double width; +public: + Square(double w) : width(w) { }; + virtual double area(); + virtual double perimeter(); +}; +</pre> +</blockquote> + +<h2>The SWIG interface</h2> + +A simple SWIG interface for this can be built by simply grabbing the header file +like this: + +<blockquote> +<pre> +/* File : example.i */ +%module example + +%{ +#include "example.h" +%} + +/* Let's just grab the original header file here */ +%include "example.h" +</pre> +</blockquote> + +Note: when creating a C++ extension, you must run SWIG with the <tt>-c++</tt> option like this: +<blockquote> +<pre> +% swig -c++ -java example.i +</pre> +</blockquote> + +<h2>A sample Java program</h2> + +Click <a href="runme.java">here</a> to see a Java program that calls the C++ functions from Java. + +<h2>Key points</h2> + +<ul> +<li>To create a new object, you call a constructor like this: + +<blockquote> +<pre> +Circle c = new Circle(10); +</pre> +</blockquote> + +<p> +<li>To access member data, a pair of accessor functions are used. +For example: + +<blockquote> +<pre> +c.setX(15); // Set member data +x = c.getX(); // Get member data +</pre> +</blockquote> + +<p> +<li>To invoke a member function, you simply do this + +<blockquote> +<pre> +System.out.println( "The area is " + c.area() ); +</pre> +</blockquote> + +<p> +<li>To invoke a destructor, simply do this + +<blockquote> +<pre> +c.delete(); // Deletes a shape +</pre> +</blockquote> + +<p> +<li>Static member variables are wrapped with java static get and set access functions. For example: + +<blockquote> +<pre> +n = Shape.getNshapes(); // Get a static data member +Shape.setNshapes(13); // Set a static data member +</pre> +</blockquote> + +</ul> + +<h2>General Comments</h2> + +<ul> +<li>This high-level interface using proxy classes is not the only way to handle C++ code. +A low level interface using c functions to access member variables and member functions is the alternative SWIG +approach. This entails passing around the c pointer or c++ 'this' pointer and as such it is not difficult to crash the JVM. +The abstraction of the underlying pointer by the java proxy classes far better fits the java programming paradigm. + +<p> +<li>SWIG *does* know how to properly perform upcasting of objects in an inheritance +hierarchy (including multiple inheritance). However Java classes can only derive from one base class so multiple inheritance +is not implemented. Java classes can implement more than one interface so there is scope for improvement in the future. + +<p> +<li>A wide variety of C++ features are not currently supported by SWIG. Here is the +short and incomplete list: + +<p> +<ul> +<li>Overloaded methods and functions. SWIG wrappers don't know how to resolve name +conflicts so you must give an alternative name to any overloaded method name using the +%name directive like this: + +<blockquote> +<pre> +void foo(int a); +%name(foo2) void foo(double a, double b); +</pre> +</blockquote> + +<p> +<li>Overloaded operators. Not supported at all. The only workaround for this is +to write a helper function. For example: + +<blockquote> +<pre> +%inline %{ + Vector *vector_add(Vector *a, Vector *b) { + ... whatever ... + } +%} +</pre> +</blockquote> + +<p> +<li>Namespaces. Not supported at all. Won't be supported until SWIG2.0 (if at all). + +</ul> +</ul> + +<hr> +</body> +</html> |