Okay - just follow up to ABs email - I had to use this last year when developing a library.
Problem is that libraries are .jar (compiled java), these have to be made in xCode (or similar IDE), then they have to be put into the correct folder for processing to be able to find them as new libraries (this requires restart of processing). So you can imagine how repetative and annoying it is to keep recompiling and updating the .jars.Way around this is to work with the sources in xCode and compile the new libraries at the same time processing starts to run.
Have inked the xCode template project for running processing sketches - any additional libraries as .jars need to go into the ‘libs’ folder, if they are .java (i.e.ones you are working on/editing etc.) the need to go in ’src’ with your main processing sketch file.