According to Apple, I should switch from Java to Objective-C if I want to use the Cocoa Framework.
Accorind to me, I'd rather start with a more 100% java app and put some Mac features in, using JNI. I want to move away from dependence on Cocoa which is proprietary and move to something that is cross-platform, such as Swing, and add some features to make my app somewhat Mac-like.
I really don't want to give up on Java now that I know it somewhat and start over with Objective-C which is more proprietary.
There are a number of ways of making a Java desktop application behave more Mac-like, and making use of some OS X capabilities that normally are out of reach of Java. The MacOsxFaq contains a number of links to resources in this area. In particular, check out OSXAdapter, and Greg Guerins software if you want to go down the route of using JNI.