1. Have a look with the ant documentation.
The copy task allow you to have "filters" that pick things like @AAA@ in the source file and replace these element with something more appropriate.
For instance, you may have @COPYRIGHT@ somewhere in the source-code that will be replaced by the real copyright notice in the generated source-code.
2. Source is everything. For that reason, programmers should always put good comments in their code ;-)
As mentioned above these are filter tokens. There purpose here is to allow for JDK 1.3.x & 1.4.x support out of the same build system. Since the Java language does not provide a preprocessor we had to use Ant and the copy task w/filters to preprocess select sources.
I think it is sorta funny, this preprocessor thing... the designers of Java deemed a preprocessor as uneeded due to Java's portability (across systems). Yet, it seems they have over looked the need for portability between versions of Java!
Bah, silly designers.