Why is the Classpath exception necessary?
If an application needs to be distributed with parts of NetBeans under GPL v2, that application could be subject to the requirements of the GPL that all code that is shipped as part of a "work based on the GPL program" also be GPL licensed. Accordingly, a GPL license exception is needed that specifically excludes from this licensing requirement any application that links to the GPL implementation. The Classpath exception accomplishes this. This would be, for example, important for module developers, that are always linking with NetBeans APIs, but also for those that build applications on top of the NetBeans Platform.