New to Java

Hello everyone,

I'm still rather new to Java but have managed to finally pull off one of my first applications (which I intend on selling). Now that the application is complete, I'm faced with the task of securing it. Now I'm pretty knowledgable in online security, but securing applications is something completely new to me, especially in the Java area. What precautions do I need to take and what's a few good security measures I can take to prevent my JAR files from being cracked/reversed? Is there any libraries or tools out there to help secure my application? I was thinking of doing a licensing system, but I'm not clear on that yet.

Any input is greatly appreciated. Thanks.

Regards,
Josh