how to build gatk?

I'm trying to build gatk from the source but I can't find any guides on this.
I tried cloning the git:
git clone git://github.com/broadgsa/gatk-protected.git
then running "ant" from that directory. What am I missing?

I get a bunch of "illegal start of type" errors and then this:
BUILD FAILED
/home/paultanger/gatk-protected/build.xml:453: Compile failed; see the compiler error output for details.