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Event Handling

Vegad Arvind
Ranch Hand

Joined: Jan 10, 2001
Posts: 42
Hi,
Que from IBM moc
Based upon the code below, which of the answers apply?
1. public class TestFrame extends Frame {
2. public TestFrame(String title) {
3. super(title);
4. enableEvents(AWTEvent.WINDOW_EVENT_MASK);
5. }
6.
7. public void
processWindowEvent(WindowEvent we) {
8. System.out.println("Window event processed");
9. }
10. }
a) The window listener that has been added to TestFrame will be called on every window event.

b) This code will compile and run if a window listener is added to an instance of TestFrame.

c) An exception will be thrown if a window listener is added to TestFrame.

d) The window listener that has been added to TestFrame will never get called.

e) This code will not compile if a window listener is added to TestFrame.


Multiple Select - Please select all of the correct answers (this question has 2 correct choices).

can anybody pls. explain.
Thanks
Avi
nan sh
Ranch Hand

Joined: Jan 05, 2001
Posts: 167
To use enableEents(AWTEvent.WINDOW_EVENT_MASK),
you must call super.precessWindowEvent(e),
otherwise actinPerformed() never
will be called, so line 7-9 should be;
7. public void processWindowEvent(WindowEvent we) {
8. System.out.println("Window event processed");
9. super.precessWindowEvent(we)
10. }
So that d) is the answer, and b) is correct too,
as you can have more then one Window listener.
see R&H book p354 for more details.
correct me, if i am wrong.

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Navin Narayan
Greenhorn

Joined: Jan 25, 2001
Posts: 25
Hi nan,
You are right except for this we are
"To use enableEvents(AWTEvent.WINDOW_EVENT_MASK),
you must call super.precessWindowEvent(e),
otherwise actinPerformed() never will be called"
It is not to use enableEvents(AWTEvent.WINDOW_EVENT_MASK)
that we call super.precessWindowEvent(e), but only to invoke the super class's method which informs all the registered listeners about the event and calls their actionPerformed(e).
Regards,
Navin
 
It is sorta covered in the JavaRanch Style Guide.
 
subject: Event Handling