Completing a Standard Window

Serial version UID

Some development environments display a warning for any class that extends a windows component, stating that “The serializable class does not declare a static final serialVersionUID of type long”.

1. Add a private static final long instance variable called serialVersionUID with a value of 1L.

...
public class WizardOfYesNo extends JFrame {
private static final long serialVersionUID = 1L;
private static final String[] ANSWER = {"Yes",
...

Running the program should produce the same results as before.

Event queue

Did you notice the import statement that Eclipse inserted for JFrame? The import statement shows JFrame is in the javax.swing package. Therefore, JFrame is a Swing component. Java expects all Swing objects to be created on an event queue.

Create WizardOfYesNo on the EventQueue

1. Replace the code in the main() method with code exactly as shown.

...
public static void main(String[] args) {
   EventQueue.invokeLater(new Runnable() { public void run() {
          new WizardOfYesNo();
       }
   });
}
...

The program should still run with the same results, but may now run faster.

Cross-platform look and feel

Windows, dialogs, and the components they contain, look different on computers with different operating systems. This difference affects how code should be written. In order to get program code in this course to work the same, regardless what operating system you are running on, use the Cross-Platform look and feel.

Use the cross-clatform look and feel

1. Add a try/catch block to the beginning of main().
2. In the try block, create a new string called className, initialized by getting the cross-platform look and feel from UIManager. (Hint: use UIManager's getCrossPlatformLookAndFeelClassName() method.)
3. Set the look and feel with className. (Hint: use UIManager's setLookAndFeel() method.)
4. In the catch block, catch any Exception and do nothing when the exception is caught. (Hint: catch Exception. Hint: do nothing by using empty brackets, {}).

...
public static void main(String[] args) {
  try {
    String className = 
    UIManager.getCrossPlatformLookAndFeelClassName(); 
    UIManager.setLookAndFeel(className);
     }
  catch (Exception e){}
  
  EventQueue.invokeLater(new Runnable() { 
    public void run() {
          new WizardOfYesNo();
            ...

The window should now have the standard Java metallic look and feel.