J2SE 1.6, which is scheduled for a beta release this fall with general availability eyed for 2005, is slated to feature an isolates function to boost application-sharing in the JVM, according to Murali Kaundinya, senior Java architect for Sun Software Services. The isolates capability would enable isolated entities to perform localized computation without requiring a second JVM, thus enabling multitasking within the JVM, according to Kaundinya.
This means that Java libraries can be shared between running Java applications and thus reducing their memory footprints and probably boosting performance aswell. Originally this was already planned for J2SE 1.5 I believe. Anyway, Apple's JVM already does this in their J2SE 1.4 version.