Intro. Sorry, I jumped in this question without taking time to read it in details. Since you are new there must be more to say in order to create an helpful answer. And I prefer to create a new one instead of editing the first one.
The easy way,
If you do not want to change so much:
You can try to remove the static fields. Ideally, nothing should be static ...
I'm going to answer my own question. Never do this!. I have just tried saving a new Filefilter object with this filter:
.addFilter("Delete files, Delete all files",f->f.delete());
And when selected, it deletes all the files in the current directory.
About the code itself, you should try to separate the view from the "logic" by applying one of the various patterns (MVC and MVP being the most used), as said by Gilbert La Blanc in his comment,
About the visual part, it is easier to create components that provide high level functionality(ies) and that you use to compose your main view.
For the &...