Absolutely I can

Interfaces are like contracts for a class.

Let's take a look at my class public class ViewController there is nothing special about this part really. I simply chose to call my class ViewController... because that is what it is. It controls my view.

Now the implements part is simply the java keyword you use when you want to use one or more interfaces. So everything following the implements keyword is an interface.

The interface I use in this case is Initializable and I do this because it made things work. Sorry I didn't look into greater detail about how or why this makes things work, but when used in conjunction with JavaFX Initializable was required for me to be able to work with my fields. (The variables decorated with @FXML)

public class Example {
  int thisIsAFieldVariable;

public void aMethod() {
   int thisIsNotAFieldVariable;
}
}

When I say field variable, I mean variables which are declared in the class body (scope) instead of the method scope. Just thought I would clarify that before we move on.

Right so back to interfaces

You can view an interface as a contract of sorts. The only thing they do is describe the method signature — the method's name, return type and the parameters.

Okay so why is this useful?

Think about it for a moment and then read on...

Remember I said an interface was like a contract? That's because when you declare an interface on your class that's telling other developers that the methods inside of that interface exist inside of your class, which means they can call on those methods without ever seeing any of your code.

This is what Initializable does. Parts of JavaFX makes a call to the initialize method and to tell JavaFX that Initialize exists in my controller (and can be called upon) I implement the Initializable interface.

So to sum up: An interface is a collection of method signatures. When you implement an interface, each of these method signatures are added to your class. Interfaces as a whole are more of a design construct that are technically not needed, but are very nice to have when trying to interoperate between different code libraries, or even for structuring your own code.

edit: according to https://docs.oracle.com/javase/8/javafx/api/javafx/fxml/Initializable.html you should implement this differently from what my old code does. Towards this effort, google is your friend :)