jRRD cannot and will not write rrd files. We think that RRDTOOL is the good tool to create and update pure rrd files.
Because you may need to read data from rrd files to display them in you java app without having to call an external process through JNI or a web call to some CGI provided by RRDTOOL
The current version of jRRD is very close to a straight port of the c code of rrdtool. We will try to put some more OO in the future.
The initial release of jRRD was in 2001. The second release of jRRD was produced (officialy) in 2009. We took the decision to leave java 1.4 behind us. If you really need a java 1.4 compliant code, feel free to checkout the svn code and try to compile it with a java 1.4 compiler.