Re: I need a different approach - suggestions please

Lew <>
Wed, 27 Jun 2012 18:54:21 -0700 (PDT)
bilsch wrote:

Lew wrote:

There are a few mistakes in your code.

You don't need to call 'super()' in the constructor explicitly.
That's what happens by default anyway.

You called the constructor directly from the 'main()' routine. That means
you called it from the primary thread of the program. You don't know this
yet, probably, unless you've already studied concurrency in Java a little bit.

The problem is that the GUI won't work right if you do that. You have to
move GUI actions onto the "Event Dispatch Thread" (EDT), a background
thread that the system creates to handle all GUI actions.

Also, you start all the action from the constructor. That's bad. As its name
implies, a constructor's purpose is to _construct_ an object, not run its logic.
Run the logic after construction completes and the instance is no longer in a
partially-built state.

And make your indentation consistent with the Java coding conventions (available
on line).

So all together, you'd do something like:

  public static void main(String[] arguments) {
     java.awt.EventQueue.invokeAndWait( new Runnable() {
         @Override public void run() {
              CalcGUIQ1 calculator = new CalcGUIQ1();

With help I've gotten some errors out of the program but I have reached
a point where something just won't work how it should. Your comments

What doesn't work, and how should it?

here lead me to believe the reason is the basic way I have things laid
out. But I don't know how to:

 > move GUI actions onto the "Event Dispatch Thread" (EDT), further I
dont know how to write an EDT, or what specifically are 'GUI actions' as
opposed to other lines that relate to the GUI.

You don't write the EDT. Did you read the tutorial link I provided?


GUI actions are all things that happen on the GUI, such as creating
a 'JFrame', calling 'pack()', playing with 'Graphics', or anything else that
is part of the GUI. Non-GUI actions are things like writing files, calculating
values, updating the logical model, or anything else that is not part of
the GUI.

Do please read the tutorial to which I linked. There's a reason I provided
that link.

Also, I thought the stuff I have in the constructor belonged there.

Not all of it. The program itself must run from a *completely*
constructed object. You start the program from inside the
constructor, therefore it is running on an *incompletely*
constructed object.

I dont know where to call the constructor from if not from 'main'.

You should call the constructor from 'main()', provided you properly
guard it inside the 'invokeAndWait()' call.

Why did you think I recommended otherwise?

I did some reading about threads being unsafe.

It would be very helpful to me if you could show how to rearrange the
code like you say would be better. If you have the time, it would be
very helpful. Thanks.

What was wrong with what I already showed you (and you quoted)?


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