interface ISyntaxHighlighter
{
    ...
}


class PerlSyntaxHighlighter implements ISyntaxHighlighter
{
    ...
}


How does the application know when to use a new plug-in class?

How can the application instantiate a new plug-in class?

At installation time the plugin must register with the application.


class SyntaxHighlighterRegistry
{
    ...

    void RegisterSyntaxHighlighter(String name, String className,
                                   String[] fileExtensions)
    {
        ...
    }

    ISyntaxHighlighter CreateSyntaxHighlighter(String fileExtension)
    {
        // use reflection API to instantiate the appropriate plug-in class
        ...
    }

    void UnregisterSyntaxHighlighter(String name)
    {
        ...
    }

    void Load(File file)
    {
        // load configuration from XML file
        ...
    }

    void Save(File file)
    {
        // save configuration to XML file
        ...
    }
    
}


<syntax-highlighter-registry>

    <syntax-highlighter name="c++" class="CppSyntaxHighlighter" 
                        extensions=".cpp .cxx"/>

    <syntax-highlighter name="java" class="JavaSyntaxHighlighter" 
                        extensions=".java"/>

    <syntax-highlighter name="perl" class="PerlSyntaxHighlighter" 
                        extensions=".pl"/>

</syntax-highlighter-registry>