Java special class "e" vs alias/reference variable

These are great questions.  They're so technical!  The details might make more sense when you experiment with lab 4, since you'll have all the methods and classes available to you (although in the context of banking software).  But I'll try to clarify what's happening in the case of Java Puzzle Ball.

The code on slide 4 is a slightly shorthand way of writing the lambda expression.  It could also be written as:

blade.setOnMousePressed((MouseEvent e) -> setDirection(Dir.NE));

e is the reference variable used to represent an instance of the special class MouseEvent.  I may have said "event" in the video, just as general term to mean any event when the mouse or keyboard is pressed.  We could name the variable anything: a, b, c, d, e...  I chose e just to re-enforce that it's an event.  The field blade is an instance of an ImageView.  ImageView is a special type of object in JavaFX,  Adding this component to the Ball class makes the ball clickable and capable of detecting mouse presses.   ImageView is going to be a lot like the Button fields you'll encounter in Lab 4.  Once the mouse press is detected, the lambda expression is free to call whatever methods it can.  setDirection() just happens to be written in the Ball class.

The code on slide 9 is also a slightly shorthand way of writing the lambda expression.  It could also be written as:

bumperList.stream()    .filter((Bumper b) -> b.getShape() == shape.STAR)    .forEach((Bumper b) -> b.setShape(Shape.RECT));

b is the reference variable used to represent an instance of a Bumper.  Much like the abstract Account class, this scenario assumes there's an abstract Bumper class which all types of bumpers inherit from.  We could name the variable anything: a, b, c, d, e...  I chose b just to re-enforce that the stream is dealing with a bumper.  We're able write the shorthand version of this code and omit declaring b a Bumper because the ArrayList<Bumper> bumperList is already understood to contain only Bumpers.  Obtaining the shape of a bumper is done by calling its getShape() method. This will be a lot like how Lab 4 requires you to call the getBalance() method on an account. The getBalance() method is written in the Account class, like how getShape() is written in the Bumper class.  In order to call this method from another class (like from the ButtonController class) you need to use the dot operator on an instance of an account.

Does that help?  I hope I didn't get too confusing.

Nick

Thanks!  Glad I could help clarify.

I prefer the minimalism of the shorthand version, but the longer version does re-enforce helpful information...  I'm not sure which one is "normal".  Sometimes, programming styles are just a matter of personal preference.

Have you seen the HBO show Silicon Valley?  There's a scene in Season 3 where a couple breaks up because they disagree on whether to use tabs or spaces while programming: https://www.youtube.com/watch?v=SsoOG6ZeyUI&t=30s

Nick

Congratulations!

I think it would be fine to go over a couple quiz questions.  The scenario that I'd want to avoid is when someone posts all the answers to a quiz.

Impressive!  Yes, I think your observations are absolutely right!

Nick