In case I'm not the only person who wanted a copy of just the 2013 Java WPILib source code for reference, without having to install the development tools on my computer, here's what worked for me:
1) download the file "NetBeansPlugins20130105v407.zip" from
http://firstforge.wpi.edu/sf/frs/do/...etbeans_update
2) If you don't already have
7zip, download and install it. You'll be glad you did. It can unzip anything.
3) use 7zip to drill down through the 13 (!!) directories as shown below, where, at the end of the rainbow, you will find the Java WPILib source code. Save that folder and delete all the other stuff
NetBeansPlugins20130105v407\
dist\
edu-wpi-first-squawksdk\
netbeans\
modules\
edu-wpi-first-squawksdk.jar.pack\
edu-wpi-first-squawksdk.jar\
lib\
wpilibj.src\
edu\
wpi\
first\
wpilibj