title: Plugins to add features to java
body: <p>I'm working on a project that requires to add some features to an existing java application using Netbeans. After searching the net, i founded that I should use "plugins". I didn't hear of plugins before. 
  I have a java application that I should download it from the net, then lets say I have to add a button, when clicked, calls a function that is written in some class in the application. In other words I want to make a new class that is able to access the classes and functions that are written in this application.</p>
  
  <p>What I understood from searching the net is that:
  -In the downloaded project's folder there is a folder named plugins.
  -This folder contains zip files that contains classes and other stuff.
  -I should make a plugin and add it to this folder in order to add a specific feature to the application.</p>
  
  <p>That's what I know, if there is something wrong in what I said, I'll be thankful to correct to me.</p>
  
  <p>Now, my question is that I want a link or website that can teach me how to create and add a plugin to an existing java application. Thank you :)</p>