well, you wrote, that you can't connect do DB2 with your Java application ... Same for me here, too.
Did you already find a solution for that (I know, that this thread is already a couple of months old, but I just came to get my MacBook and I'm doing my first steps).
I can connect to my DB2 10.1 with db2 command line tool but I can't use for instance the Database Explorer that is shipped with (My)Eclipse - which a Java application. Also - after setting the Oracle Compatibility - I cannot connect with clpplus (which in turn uses Java as well).
Here's the information I have on uninstalling DB2 Express-C on Mac. It assumes a slightly older version, but the steps should still be the same:
The db2_deinstall script is usually the recommended method for uninstalling DB2, however there are some outstanding issues with the db2_deinstall script on Mac OS X. Until these issues are fixed, you can uninstall DB2 manually by deleting the directories where DB2 is installed. If you performed an Admin user install, you need to remove the DB2 install dir as an Admin user by running sudo rm -rf <DB2 installdir> from the Terminal command line.
Delete the following directories.
DB2 install dir (eg /opt/ibm/db2/V10.1 for Admin user installs, ~/sqllib for Standard User installs)
Now that Apple and IBM have declared themselves partners, when will an official DB2 Express-C installation package be made available for OS X 10.10.x? It only makes senses for IBM to officially support it so Mac users can develop databases off-line that run natively on Apple hardware. Oracle gave up on Macs years ago but it looks like there might be a future for IBM databases running on Macs without virtualization or from the cloud.