Lab 15: GUI Part II

The goal of this lab is to design windows requesting input from the user.

1. Introduction and setup

Today we go back to a simulation of the same sort as the predator-prey example and the ball-catching project. We will have a grid inhabited by agents, each acting in their own way.

The grid we'll be working with today will be inhabited by Skeets. A Skeet is an object that moves about the grid in a way determined by the following parameters:

• A direction. Just like the balls in the ball-catcher example, a Skeet is going in a certain direction. The direction will be represented in radians, the same way polar coordinates are specified: 0 (or 2 pi) means straight east, .25 pi means north east, .5 pi means straight north, pi means straight west, etc.
• A velocity. A Skeet has a speed in terms of the number of grid positions per unit time. We will keep this as a double, and it will refer to the distance the Skeet will try to move in its direction. Of course, the Skeet actually moves a certain amount in the x dimension and a certain amount in the y dimension. The change in x and y are calculated from the velocity and direction (don't worry, I've already programmed that part for you).
• A rotational velocity. A Skeet is also constantly turning. During every move, it changes its direction by a constant amount, which is its rotational velocity. The rotational velocity is also expressed in radians. (A Skeet whose rotational velocity is 0 is moving in a straight line.)

Make a directory for this lab and copy the appropriate files from the course directory.

cp /homes/tvandrun/Public/cs235/lab15/* .

Then compile and run the program Skeets. Notice that there is a jar file; you'll need to refer to it on the command line when you compile and run.

javac -cp simulation.jar:. Skeets.java
java -cp simulation.jar:. Skeets

By default there is a single Skeet. If you inspect the code in Skeets.java, you'll see that the Skeet is added to the grid in the line

model.setAgentAt(100, 100, new Skeet(100, 100, .25 * Math.PI, .125 * Math.PI,
                                     3, Color.RED, model));

Compare this with the file Skeet.java, particularly the instance variables and constructor, to understand all that this means.

The intent of this program is to allow the user to add new Skeets to the system as the simulation runs. Pressing the button Add Skeet should launch a dialog box asking the user for all the specification of the Skeet and add that Skeet to the grid. However, when you press the button, nothing happens. That's for you to write.

("Dialog box" is not meant to be a technical term; it just means a smallish window on the screen temporarily to get input from the user.)

2. The AddListener class

The Add Skeet button has an action listener attached to it. However, the actionPerformed() method is empty. Your main task is to fill in this method, which will prompt the user with a dialog box.

As you add things to the window in your program, I recommend that you periodically compile and run the program to see how the window looks so far and make some adjustments. Make the window look reasonably nice; play with the dimensions and the layout until it looks right.

Here are things that ought to be in the dialog box:

• First, we want the user to be able to choose a color for this Skeet. The easiest way to do this is to use a new Java GUI class called JColorChooser. This displays a color palette which the user may click on to select a color. Then the program can read that color from the JColorChooser object. Go to the Java API to find out more about this class. Mainly you will want to use the no-parameter constructor and the method getColor().
• There must be textfields for the direction, rotational velocity, and the velocity, as well for the initial x and y position. Since it will be hard to indicate a value including pi when entering a direction or rotational velocity, you should interpret the user's input in these fields as a coefficient of pi. In other words, if the user enters ".5" into the direction field, you should interpret that to mean ".5 pi". Also, all these text fields should have an accompanying appropriate label.
• There should be a button for the user to press when the dialog is finished, labeled something like Ok.

The actionPerformed() method should also make the dialog box appear and it should attach another action listener to the Ok button, but that action listener will be the subject of the next part.

3. The other action listener class

Write another class, also implementing ActionListener which will react to the Ok button being pressed. Specifically, the actionPerformed() method should

• close the dialog box (to do this, call setVisible(false).
• read information from the textfields of the dialog box.
• add a new Skeet to the grid.

First, you should think about what pieces of information this action listener needs to know (hint: a lot). These will become instance variables and parameters to the constructor. Then writing the actionPerformed() method will be easier.

4. Turn-in

Please email the files you wrote or modified to Sarah.Cobb@my.wheaton.edu.