I'm trying to figure out where java Applets that I run from the browser get downloaded to. I'm using Firefox 3.0 on Windows XP with Java 1.6 if that makes any difference.
From the Java Control Panel on the toolbar, I can access "Temporary Internet Files -> Settings" to find the Java cache. From there I can show the resources and see a file called "dws2010066.dat". Does this resource correspond to a file on disk? I did a search in the Java cache (and my whole computer) but came up empty handed.
I remember a recent SO answer that mentioned that Windows does clever stuff to obfuscate the real file names and locations of temporary internet files. I believe that this is an attempt to make life hard for malware. That would explain why the file does not show up in a search.
As @leonm says, if you just want to get hold of the applet JAR file, why not just read the HTML file, find the link to the applet and download it using wget or an equivalent tool.
If you're interested in algorithm of code that isn't obviously available you should contact the author of the applet.
Please be careful as decompiling to copy algorithms is usually covered by copyrights and other laws.