Name: KEY CMPS 109 Quiz 4  February 25, 1999

This is a closed notes, closed book exam.

THERE ARE PROBLEMS ON BOTH SIDES OF THE PAPER

• (1 pt) What class is used as the top level ``window'' in most stand along Java applications?

  java.awt.Frame

• (1 pt) How does an event listener, listening to multiple sources of the same type, know where the event came from?

  If e is the event object passed to the listener, then e.getSource() will return a reference to the source of the event.

• (1 pt) What is the default layout manager for a Frame object?

  java.awt.BorderLayout

• (1 pt) Why does SimpleDrawApplet, draw on an Image instead of directly on the Applet, when a mouse dragged event is detected?

  The image is used to remember all drawing operations, otherwise when the window was repainted due to be covered/uncovered, iconified/deiconified etc., all of the results of the drawing operations would be lost.

• (2 pts) Describe in words and pictures what the program Quiz4 (shown on a separate page) will do. You should draw a picture or pictures to show what the screen will show and use words to say when the various pictures will be displayed.

  The initial screen has the ``Do It!'' button at the top center and a large white area below that containing ``Click Do It! when ready'' somewhere near the center. When you click the button it button label changes to ``UnDo It!'' and the area below the button all turns black. Clicking the button again returns to the original screen. This cycle will repeat as long as you click the button.

• (2 pts) What would happen to the program Quiz4 if the two methods, getMinimumSize() and getPreferredSize() were deleted from MyCanvas?

  The Frame would shrink down to be just big enough to show the button.

• (2 pts) What would happen to Quiz4 if the call to theCanvas.repaint() was deleted from DoIt? Specifically, when if ever would the paint() method in MyCanvas get called without the repaint() call?

  The initial screen would appear as described earlier. However, clicking the button would not cause the large black area to appear, only the button label would change. Anything that caused the Frame to be partially obscured and then uncovered would cause paint to be called and the appropriate screen shown (either all black or with the text message near the center).

• (2 pts) Modify the program Quiz4 so that it contains a second Button labelled ``Quit''. When the button is clicked the program should exit. You are ONLY allowed to modify the method main() in Quiz4. You are not allowed to modify any of the other classes. You can add an additional class if necessary. You do not need to write down all of main(). Indicate your changes or added lines by showing the unmodified line before your changed or inserted line. For example, if you wanted to add a line after the last statement in main() you would write:

  display.show();
  /* your new line here */
  
      Frame display = new Frame("Quiz4"); // from original
      Button quit = new Button("Quit");
      Quitter goodbye = new Quitter();
      quit.addActionListener(goodbye);
      display.add(quit,BorderLayout.SOUTH);
  
  
  /*new class*/
  import java.awt.*;
  import java.awt.event.*;
  
  class Quitter implements ActionListener
  {
    public void actionPerformed(ActionEvent e)
    {
      System.exit(0);
    }
  }