I am a novice Java coder. And I am having trouble finding the problem when I start up the program and click the "list files" button, and there are more than 37 files or more to load. It crashes and gives me a null pointer exception at line 77 in the Displays class. Any help would be greatly apreciated. I am still in the process of writing it. So any half finished code is supposed to be that way.
The source code is here: