Lab 8: Event-Driven Programming

Copyright RIT 2009
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Goal

  1. To learn how to write a Java program that responds to events
  2. Gain experience writing event-driven programs
  3. Learn how to use basic Swing events
  4. Gain additional experience working with basic Swing components

Team Setup

You are to work on this lab completely on your own.

Overview

In last week's lab you learned how to use Swing to build simple graphical user interfaces. Although the GUIs you built were neat, they did nothing. In this week's lab you will implement event-handling code to produce a functioning version of the Lotto GUI that you laid out components for in last week's lab. You will be making use of ActionEvents from JButtons, and creating listeners that handle these events appropriately. You also will be making use of the Java Collections framework to store and compare selected and winning lotto numbers.

Pre - Lab Work

  1. Review your class notes on Java Swing.

  2. Read through the Java tutorial trail on How to Use Actions (http://java.sun.com/docs/books/tutorial/uiswing/misc/action.html) .

In-Lab Activities

Activity #1 : Picking Numbers

In last week's lab you wrote a program to create and display a GUI similar to the one shown below:


Lotto start

An important step in design for programs with GUIs is to decide on the underlying model for the data that the interface will be used to view and manipulate. This model will be implemented using some variety of variables and data structures along with associated operations (e.g. mutators and accessors). We have included a couple of methods in the LottoGUI Javadoc, that you must implement as part of your design, but feel free to add additional methods if you like.

Our model here is simple. We need data structures to represent which numbers have been selected and the winning numbers, which will allow these to be easily compared to determine which numbers they have in common. You will need to think about which data structures in the Java Collections Framework are well-suited for this. In our model we will also need to represent the players' current balance, and the current state (mode) of the game.

Once you have chosen a representation, it is time to add some functionality to the number buttons. When a JButton is pressed, an ActionEvent is generated. A GUI can capture button clicks by creating and installing an ActionListener. Normally one ActionListener will handle the ActionEvents generated for a group of buttons. The ActionListener can determine which button was pressed by invoking the ActionEvent's getActionCommand() or getSource() method. To implement the ActionListener interface, we need a single method, actionPerformed(). You may choose to have your LottoGUI implement this interface itself, however eventually we will have several different types of buttons to react to. Therefore, you may prefer to implement ActionListeners for different types of buttons with inner classes or anonymous classes.

In the LottoGUI, you should handle events from the number selection pad so that:

  1. Clicking on a number turns the button's background blue, and adds this number into the selected numbers
  2. Clicking on a selected (blue) number will turn the button's background back to the default color, and remove this number from the selected numbers
  3. If six numbers have been picked, then the user cannot select additional numbers.

Here is what the pad looks like after selecting three buttons:


Lotto pick

Make sure to implement and use the static initializeButton() method. Often in GUI programming there are a lot of initialization operations that are repeated. Methods like initializeButton() make code easier to read and maintain, by representing common sequences of initializations as one operation.

How To Submit

Once you are convinced that your program is working correctly, and that the GUI is handling the window closing event correctly, submit your work using the following command: 

try grd-232 lab8-1 LottoGUI.java *.java

Activity #2 : Adding Additional Button Functionality

In this activity, we will implement some functionality for the "Reset", "Quit", and "Draw" buttons. The "Quit" button should close the main window using the dispose() method of JFrame. Closing the window should also make the program stop. You can make this action occur by changing the default close operation of your GUI window.

"Reset" will deselect all numbers, in the GUI turning their associated button's background color back to the default. The "Draw" button should become active when six numbers have been picked (the letters in "Draw" turn green). If the user deselects a number after six picks, "Draw" should become inactive again.


Lotto ready

When the "Draw" button is active, if the user clicks on the button, six winning numbers are chosen at random (see the Math.random() method), and the player loses $1 (the cost of one play). The selection of the numbers is done using the pickWinner() method. Clicking 'normally' on draw when it is active should invoke pickWinner with the argument 'false,' to choose the winner in this way.

However, the user may also cheat by clicking on the active "Draw" button while holding down the shift key. This results in the function 'pickWinner()' being called with the argument 'true.' This causes the winning numbers to match the currently selected numbers. The ActionEvent class has a routine called 'getModifiers()' that returns a value indicating what modifier keys are held down. The constant ActionEvent.SHIFT_MASK is used to indicate that shift key was held down during the event. If you perform bitwise and (&) with the current modifer value and the shift mask, you can tell whether the shift key is pressed.

For this activity, it is sufficient to simply print the selected and winning numbers when "picked" to the standard output.

How To Submit

Once you are convinced that your program is working correctly, submit it using the following command: 

try grd-232 lab8-2 LottoGUI.java *.java

Activity #3 : Playing the Lotto

Now we will fully implement the "Draw" operation so that we can actually play the game. In the last activity we implemented "Draw" so that we can select winners numbers (whether fairly or not-so-fairly). In addition to losing $1 each time we press "Draw", we will now implement the payoffs. Your program will now determine how many selected numbers match winning numbers, and pay out accordingly. The two possible outcomes are:

  1. All six numbers match. The "Picking Numbers..." mode status changes to "Win!", and the player's balance is increased by twice the number of matches ($12).
  2. Between zero and five numbers match. The mode status changes to "N numbers matched" (where N is the number of matches), and the player's balance is increased by the number of matches ($N). Notice that we break even if we match one number.

The user is shown which numbers were picked in the following way: Winning numbers that match selected numbers are shown in green, while winning numbers that do not match selected numbers are shown in red.


Lotto matches

It is important that the player must not be able to change the state of the buttons by clicking on them at this point; only hitting the "Reset" button should return all the number pad buttons back to their default colors, set the mode status message back to "Picking numbers...", make "Draw" inactive, and allow the user to play again.

For this program, we will allow negative balances for the player; they can keep playing into negative numbers if they choose.

How To Submit

Once you are convinced that the program is working correctly, submit it using the following command: 

try grd-232 lab8-3 LottoGUI.java *.java

Grade Computation

Grade Breakdown: