If you create a PrintWriter object, which I think is still in the processing api you can append a character sequence to it (including StringBuilder). However you may be better off checking out regular java io, depending on what you wish to achieve (you definetly need not cast to String before writing to output that would be daft).

1.   PrintWriter pw = createWriter("test.txt");
     StringBuilder fred = new StringBuilder("fred and others");
     pw.append(fred);
     pw.close();
   

Works!!!

Thanks, I saw your post from years ago that alerted me to StringBuilder. While waiting for responses I did this;

My concern with the PrintWriter is that it is "text" and I am not sure which limitations that imposes.