Plugins are written to enhance JIRA's functionality. There are many tutorials available and for me, the simplest one being adding your own menu item.
There is also a simple tutorial I have written which you might find helpful.
Let us know if you need any help.
To answer your question where to store java code?
When you create a jira plugin module, you enter the class name and package name. You will find these .java files created under your plugins /src folder where you can write your own implementation.
Hello Atlassian Community! Each month, we run a series of Spotlights to highlight Marketplace vendors and apps that our team thinks this Community would find valuable. In last month's Spotlig...
Connect with like-minded Atlassian users at free events near you!Find a group
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no AUG chapters near you at the moment.Start an AUG