how to build a JAR

I don't understand how or why GNU is building JAR's the way it does.  
Perhaps there's an historical or political reason?

Generally, ant is used to build Java projects and package them as JAR's, 
but GNU seems to be using make(?).  Why is this so?

The INSTALL file states:

Ant build

A simple Ant buildfile is included for platforms where GNU Make is not
installed. This buildfile is not officially supported and may not provide
options available during the standard autotools-based installation.



I'm just curious because this seems at odds with other Java projects I'm 
familiar with.  Specifically I'm interested in checking out a module, 
the mail module, forking the code a bit, and building the corresponding 
JAR.  However, I'm really clear on what code *to* check-out and which 
JAR it should build to.


Any help appreciated.



thanks,

Thufir