Java Jlabel-使用setText时不显示文本

Question

When modifying lblError I am using set text. It is working in my try catch statements just fine. But when I am running an else statement and it enters the else statement...(I have checked) the setText doesn't make the label display the text I want it to

it works ehn this code is implemented:

try {
    Schedule newSched = ScheduleReader.read(text);
    for (int i = 0; i <= newSched.getLastFlightTime(); i++) {
        ArrayList<Flight> flightsAtTime = newSched.getFlights(i);

    for (Flight f : flightsAtTime) {
         s.add(f);
        }
    }
    flights= getArrayList(s);
    displaySchedule();
    lblError.setText("");

   } catch (IOException e1) {
    lblError.setText(IO_MESSAGE);
   } catch (FormatException e1) {
    lblError.setText(FORMAT_MESSAGE);
   } catch (DuplicateFlightException e1) {
    lblError.setText(DUPLICATE_FLIGHT_MESSAGE);
   }
}

but it doesn't work when I do:

 else{
        lblError.setText(FLIGHT_NOT_READY);
    }

Answer 1

Then either 1) the else statement is never called or 2) you're calling the method on a different JLabel object from the one displayed.

To test the first, do:

else{
   System.out.println("else block called");
   lblError.setText(FLIGHT_NOT_READY);
}

To test the second, check to make sure that you've not created a second instance of the class that holds the JLabel.

Otherwise, if you're still stuck, consider giving us more information and code, as I don't think we have enough to be able to tell you with complete confidence what the cause of your problem is.

Answer 2

You can't necessarily just call setText() on a visible label and have it take effect immediately -- especially if you're not calling it from an event handler. In general, if you change the appearance of a component that's showing on the screen, you must call validate() on the component to force the layout to be updated; in the case of an empty label getting new text, this is definitely going to be required.

EDIT

And @HovercraftFullOfEels also has some good suggestions of other things that might be going wrong.