Netbeans and Compiled Code

Question

(best image: http://i.imgur.com/8m53Uxr.jpg )

I opened a .java file (not .class ) in Netbeans and I came across these "Compiled Code" blocks. I was tasked with refactoring this code so that we can make some changes, but each method has compiled code blocks.

When I double-click on one of them, it expands and shows things like

 * 6: astore_2 * 7: aload_0 * 8: ifnull 93 

What is it and how should I understand what this code does? There is no documentation, and the programmer who wrote this left ten years ago, and no one knows how it works.