Java Glossary : caching

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Caching is a general term of keeping a small subset of a larger set handy for rapid access. SQL databases keep the most popular parts of the disk-based database in RAM. DNS lookup servers keep locally copies of the names it uses most frequently. Operating systems keep copies of the most commonly used parts of the hard disk in a RAM cache.

Starting with JDK 1.3 the Java Plugin offers Applet caching. This means Applets need be downloaded only when new versions have been uploaded to the server. Otherwise they are executed from a local cache. There are special plug-in commands to control which Applets are sticky and which are downloaded fresh each time.

To clear the in-RAM ClassLoader Applet cache in Internet Explorer, click Tools | Java Console | x .

To clear the in-RAM ClassLoader Applet cache in Opera, click Tools | Advanced | Java Console | x .

You can configure the cache size in a browser. Don't be crazy generous. If you choose something like 9000 MB you will eventually fill up your entire hard disk with junk you never use and your machine will grind to a halt. To make matters worse, IE cleverly hides the cached files from view that are causing all the trouble. Especially on Windows 98, to add insult to injury, having too big a cache will slow you down too. 20 to 100 MB is probably sufficient before you reap no additional benefit.

To manually clear the Applet/Jar cache, delete files in:

C:\Documents and Settings\Administrator\Application Data\Sun\Java\Deployment\cache\javapi\v1.0\jar
C:\Documents and Settings\Administrator\Application Data\Opera\Opera75\profile\cache4

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