From deep in the mists of time, up through NetBeans 3.6, the NetBeans IDE had a way of assembling the classpath for your project by mounting filesystems (think UNIX mount points). You assembled your classpath by aggregating together a pile of directories (see Figure 6.1).
Figure 6.1. Mounting filesystems in NetBeans 3.5.1
That style of UI was changed in 4.0, but the Filesystems API which made it possible is still used considerably under the hood. The Filesystems API allows NetBeans code to treat things that are not files in the
java.io.File sense (such as entries in a JAR or ZIP file) as files, so the same code can work ...