Java Cookbook

Running an Applet with a JDK

Problem

You want to use an applet on an intranet or the Internet, but it needs a modern JDK to run.

Solution

Use the Java Plug-in.

Discussion

Sun’s Java Plug-in allows your applet to run with a modern JDK even if the user has an ancient browser (Netscape 2, 3, or 4), or an anti-standard-Java browser (Microsoft Explorer might come to mind). For Netscape, the plug-in runs as a Netscape Plug-in. For Microsoft, the plugin runs as an ActiveX control. The Java Plug-in was previously a separate download, but is included in the Java Runtime Environment (JRE) in all modern JDK versions.

The HTML code needed to make a single applet runnable in either of those two modes rather boggles the mind. However, there is a convenient tool (which Sun provides for free) that converts a plain applet tag into a hairy mess of HTML that is “bilingual”: both of the major browsers will interpret it correctly and do the right thing. Note that since browser plug-ins are platform-dependent, the Plug-in is platform-dependent. Sun provides versions for Solaris and MS-Windows; other vendors provide it ported to various platforms. Learn more at Java’s Plug-in page, http://java.sun.com/products/plugin/.

To try it out, I started with a simple JApplet subclass, the HelloApplet program from Section 25.9. Since this is a JApplet, it requires Swing support, which is not available in older Netscape versions or newer MSIE versions. Here are some screenshots, and the “before and after” versions ...