"set lock mode" in java/jdbc

How do vary the lock mode in java/jdbc for Informix? We've been testing concurrency control with servlets, Apache/Jserver, IDS 7.30 and Solaris 2.6/x86 (don't ask). We've found that the default lock mode is not, or doesn't appear to be, as by convention, "not wait": We can execute a select for update (with a sleep prior to commit for testing)via one servlet, and select for update on same row in another servlet, but instead of an error message, the second will wait until the first completes, then update. Has anybody experienced this problem? I'd like to work around it by explicitly setting lock to "not wait," but haven't discovered the syntax for this. Can this be done? We're using Informix's latest jdbc driver. tia