I'm also working on this assignment, in order to increase my familiarity with NetBeans. Here are some things I've found (or think I've found) that may also help you with the assignment.

Save your work often. The NetBeans visual GUI builder is very buggy. Also, it uses some classes that are only available in Java 6.

Try to get the GUI right before you add code to it. To be extra safe, keep all your added code together in one place, and make a copy of it somewhere before you make any changes in the GUI. (I put all my additional instance variables just above my @Actions.)

The MVC design pattern says that you should keep Model, View, and Controller as separate as possible. The NetBeans GUI generator puts your @Actions methods into the View class. This is okay--keep all your added code together, and your View and Controller will still be logically separate, even if they are in the same class. The Model, as usual, should still be in its own class.

Notice the Source and Design tabs. These allow you to switch back and forth between the code view and the GUI view of your application.

When you are in the Design view, there is an Inspector pane on the left side. Double-click on any JPanel in the Inspector to view just that JPanel. Double-click on the main panel to get back to seeing the entire GUI.

In the Properties pane (on the right side) there are Properties and there are Other Properties. Presumably the idea is that the most important properties are in the first batch; if so, I don't agree.

• You should set the display panel (the one showing the animation) to have a suitable background color (probably white) for your animation.
• Your buttons should all have appropriate text. NetBeans seems to lose this text any time you do anything else to the button, so you may have to re-enter the text.
• Program variables should have meaningful names, for example, runButton instead of jButton3, and controlPanel instead of jPanel2. Changing the name field in the Properties pane should do this, but that doesn't seem to work. However, right-clicking in the Inspector pane and choosing Change Variable Name... does seem to work.
• Each button should have an associated action. Click the [...] to the right of action and, using the Default editor, choose Create New Action..., then enter the name of the method to be called when the button is clicked.

NetBeans generates a lot of code for you--some of it pretty ugly, in my opinion.

• Don't change any code in the gray areas!
• You don't need to understand much of this code. Concentrate on the @Action methods you added.
• Every JPanel has a getGraphics() method. Once you have a JPanel's Graphics object, you can draw on it.

In my Animation slides from CIT591, I use a java.util.Timer. NetBeans uses a javax.swing.Timer. It is illegal to try to import both into the same class, because then Java doesn't know which Timer you mean. There are two possible solutions:

• (Good) Import javax.swing.Timer but not java.util.Timer. Then when NetBeans refers to Timer, it gets the Swing version. When you need the older utilities version, refer to it using its full name, java.util.Timer.
• (Better) Adjust my code to use javax.swing.Timer instead of java.util.Timer. This turns out to be a little easier--instead of an inner TimerTask class, you just need an ActionListener.

I found that, with the Timer, I didn't have any need for Observer/Observable. Since I didn't use these, you don't need to, either.

There are two ways to change the speed of the animation. The simpler way is to reduce the frame rate--the longer the time interval between successive frames, the slower the animation. This has the disadvantage that the animation is very jerky at slow speeds.

The better way is to keep the frame rate high, and to change the amount that the ball (or other animation) moves between frames. If you do this, it will work much better if you keep your x,y position and your deltaX,deltaY velocity as doubles rather than as ints, and convert the position to ints as the final step.

When your program works, and you create an executable .jar from it, don't assume that the jar file works! Test it! If it doesn't run, one possible reason is that NetBeans is using some nonstandard classes that you haven't included in your jar file--most likely a layout manager. (Another possibility is that your Java installation isn't completely correct, in which case the jar file might or might not be fine.)