Lab 12 In-Class: Graphical User Interfaces

Vote Counter - Using Buttons

1. Compile the program, then use the appletviewer to see how it works (you may use the file Vote.html).

2. Modify the program so that there are two candidates to vote for -- Joe and Sam. To do this you need to do the following:
   1. Add instance variables for Sam -- a vote counter, a button, and a label. Initialize these variables in the init method.
   2. Add a new inner class named SamButtonListener to listen for clicks on the button for Sam. This will be just like the JoeButtonListener class except it will modify the variables that hold Sam's information instead of Joe's. Create an instance of this class when adding the ActionListener to the button for Sam.
   3. Add the button and label for Sam to the Container object.

3. Compile and run the program.

Greetings - Listening for Events on a Text Field

1. Save the program to your directory, compile it and run it in the appletviewer (you may use the file Greetings.html). Press ENTER several times in the text field; change the name at least once.
2. The same listener in a program can listen for more than one event. Modify the program by adding a button that, when pressed, will display a new greeting just as pressing enter on the text field does. The listener that is already defined should also listen for the button push. That is, one listener will listen for two different events -- it will respond to either event by displaying a new greeting. All you need to do is the following:
   • Declare a new JButton instance variable.
   • Create the JButton in init -- label it to let the user know that they will get a new greeting when it is clicked.
   • Create a GreetingListener object and make it listen for the button press. (NOTE: There are two ways to do this: One, do it exactly as was done for the text field -- that creates a new GreetingListener object so there will be two separate objects. The other way is to create one listener object and give it a name -- for example,

           GreetingListener myListener = new GreetingListener();
     

     then use that name in both statements that add the action listener to the component -- for example, name.addActionListener (myListener).
   • Add the new button to the content pane.
3. Compile and run the applet. You may see that the components no longer fit in the applet window (you may have seen this earlier if you typed in a long name.) If so, change the applet size -- try various sizes until you find something that looks good.
4. Test the program by both pressing enter on the text field and by pressing the button. Either event should cause a change in the message. Also try typing in a new name (but don't press enter), then clicking on the button. You will see that the new name is displayed (because the actionPerformed method gets the name from the text field each time it is executed -- the new name is there even though enter was never pressed).
5. Adding Some Color Modify the applet so that it changes colors when an action event occurs. Do the following:
   • Currently the Container object cp is a local variable in init. Move the declaration (but not the assignment that sets cp to refer to the content pane of the applet) so it is an instance variable.
   • Now, in actionPerformed, in each part of the switch statement that chooses a greeting, add a statement to set the background color of the content pane. (All Java components have a method void setBackground (Color color) that changes the background color -- see the JComponent class on pages 846 and 847). Use a different color for each of the four cases.
   • Also, change the color of the button in each of the four cases -- both the background (the button itself) and the foreground (the label on the button). Components have a setForeground method that is analogous to the setBackground method.
   • Compile and test your program. Be sure your colors look good and that the labels are visible. (NOTE: You can also change the color of your labels, such as the output label that gives the greeting.)

Computing Body Mass Index

           (703 * weight in pounds) / (height in inches)2

1. File BMI.java contains a skeleton for a GUI to calculate BMI.The user enters his or her height and weight and presses "Calculate BMI"; the program then displays the user's BMI. Much of the framework has been done for you, but you will need to fill in code. (Note that this program is much like the applet version of the temperature conversion program handed out in class. The application version of that program is FahrenheitGUI.java in Listing 5.15 of the text.) Do the following (follow the instructions and the comments in the program):

   In the init method of the applet you need to do the following (put your code for each immediately after the corresponding comment in the code):

   • JLabels have already been created to identify the height and weight textfields. You need to create a JLabel for the output, and one to hold the actual BMI. (NOTE: Use the variables that have already been declared.)
   • Create JTextFields to hold the person's height in inches and weight in pounds.
   • Create an appropriately labeled JButton for the user to press to calculate the BMI.
   • Create a BMIListener and make it listen for the button to be pressed. Note that the listener is added to the button, not the textfields, so the BMI is computed only when the button is pressed, not when the user presses Enter on the textfields.
   • Add the height label and textfield to the content pane (the content pane has already been created for you). Note that the components will appear on the content pane in the order in which you add them (left to right, top to bottom).
   • Add the weight label and textfield to the content pane.
   • Add the button to the content pane.
   • Add the label identifying the result and the label holding the result to the content pane.

   In the actionPerformed method of BMIListener:

   • Get the text from the height and weight textfields and store it in the String variables provided.
   • Use Integer.parseInt to convert the text to integer values, and store them in the int values provided.
   • Calculate the BMI from the height and weight values.
   • Use Double.toString to convert the BMI to a string, and store the string in the result label.

   Compile the BMI applet and run it in the applet viewer. You may use the html file BMI.html to run the applet.

2. (Optional) Add code to the BMI applet to let the user have some idea of what their BMI means. You need to either modify the JLabel that displays the BMI or add a new JLabel. Your program should include a message based on the following: a BMI less than 19 indicates the person is underweight, a BMI between 19 and 25 (inclusive) means a healthy weight, a BMI between 26 and 30 (inclusive) indicates the person is overweight, and a BMI over 30 indicates the person is very overweight.

HAND IN