Java Applet & JavaScript Function

Here is the situation:
I have java applet on my webpage. The applet uploads the file and
when the upload is completed it calls the JavaScript function that
is located on the same page.

For calling JavaScript function I use:
getAppletContext().showDocument(new URL("javascript:function_name('param1', 'param2', 'param3')"));

Everything works fine in IE and Firefox on WindowsXP, but in Opera I
get the following exception:
java.net.MalformedURLException: unknown protocol: javascript

On Mac + Firefox the applet does its job uploading the file
but the javascript function is not running (also no exception is
thrown by the applet)

Any ideas how to fix this?