 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
Java Forum / First Aid / November 2007exception
Good evening all, I'm taking a java class and as one of the final assignments, we've got to write a program that uses a gui with buttons. We've got to use a function that adds records. I've got this being handled by a button but i'm getting an error that I need a throws exception. As luck would have it, the instructor never covered this aspect of Java but I did find an example on google. The problem i'm having is understanding how to use it. Since my button processes the code it seems like the exception handling needs to be there. I don't know of another way to call the button other than using the listener, that triggers the event when the button is pressed. At this point, i'm stuck. Any insight about how to do this, is appreciated. This is an introductory java class so. The error message I get. ¼§ÏStudentAddWindow.java:92: exception java.io.IOException is never thrown in body of corresponding try statement private class addButtonListener implements ActionListener { public void actionPerformed(ActionEvent e) { try { String name; } catch (IOException x) { FileWriter swriter = new FileWriter("c:\\studname.txt",true); JOptionPane.showMessageDialog(null,"The file could not be written."); //name = StudentTextField.getText(); FileWriter swriter = new FileWriter("c:\\studname.txt",true); //FileWriter gwriter = new FileWriter("c:\\grades.txt",true); PrintWriter outputFile2 = new PrintWriter(gwriter); //PrintWriter outputFile= new PrintWriter(swriter); outputFile.println(name); //outputFile2.println("0,0,0"); outputFile.close(); //outputFile2.close(); StudentTextField.setText(""); } Thanks Art > [...] > The error message I get. [quoted text clipped - 12 lines] > } catch (IOException x) > [...] Well, okay, why do you thing `String name;' is going to throw an IOException? The whole inside of the try block does nothing at all -- it declares a variable `name' that can refer to String objects, but never uses it and never does anything -- so there's no way an IOException can ever be thrown. Why are you trying to catch something that cannot exist?  SignatureEric Sosman esosman@ieee-dot-org.invalid My apologies, the code for the throw was assumed. I've included it here. Thanks public void actionPerformed(ActionEvent e) { try { addingStudent(); } catch (IOException x) { String name; name = StudentTextField.getText(); FileWriter swriter = new FileWriter("c:\\studname.txt",true); FileWriter gwriter = new FileWriter("c:\\grades.txt",true); PrintWriter outputFile2 = new PrintWriter(gwriter); PrintWriter outputFile= new PrintWriter(swriter); outputFile.println(name); outputFile2.println("0,0,0"); outputFile.close(); outputFile2.close(); StudentTextField.setText(""); } >> [...] >> The error message I get. [quoted text clipped - 20 lines] > be thrown. Why are you trying to catch something that > cannot exist? > My apologies, the code for the throw was assumed. I've included it here. > [quoted text clipped - 10 lines] > > } Maybe its simpler to show how I think it should be done. public void actionPerformed(ActionEvent e) { // Dear tutor, grill student re spoonfed solution from usenet. try { String name = StudentTextField.getText(); FileWriter swriter = new FileWriter("c:\\studname.txt",true); PrintWriter outputFile= new PrintWriter(swriter); outputFile.println(name); outputFile.close(); FileWriter gwriter = new FileWriter("c:\\grades.txt",true); PrintWriter outputFile2 = new PrintWriter(gwriter); outputFile2.println("0,0,0"); outputFile2.close(); StudentTextField.setText(""); } catch (IOException x) { System.out.println("Unable to add student - " + x.getMessage()); JOptionPane.showMessageDialog(frame, x.getMessage, "AppName", JOptionPane.ERROR_MESSAGE); System.exit(1); } } Untested, caveat emptor. > Maybe its simpler to show how I think it should be done. > [quoted text clipped - 24 lines] > > Untested, caveat emptor. All that I/O - could end up being a lengthy process, ergo, a candidate to move off the EDT. SignatureLew >> Maybe its simpler to show how I think it should be done. [snip] > All that I/O - could end up being a lengthy process, ergo, a candidate > to move off the EDT. Ooh yes ... let me dig myself a little deeper ... Art, please avert your gaze ... public void actionPerformed(ActionEvent e) { // Blindly copying usenet may be hazardous to your education. frame.setCursor(Cursor.getPredefinedCursor(Cursor.WAIT_CURSOR)); final String name = StudentTextField.getText(); new SwingWorker<Void, Void>() { private IOException pendingException; @Override protected Void doInBackground() { // not EDT try { FileWriter swriter = new FileWriter( "c:\\studname.txt",true); PrintWriter outputFile= new PrintWriter(swriter); outputFile.println(name); outputFile.close(); FileWriter gwriter = new FileWriter( "c:\\grades.txt",true); PrintWriter outputFile2 = new PrintWriter(gwriter); outputFile2.println("0,0,0"); outputFile2.close(); } catch (IOException x) { pendingException = x; System.out.println("Unable to add student - " + pendingException.getMessage()); } } @Override protected void done() { // on EDT frame.setCursor(null); if (pendingException == null) { StudentTextField.setText(""); } else { JOptionPane.showMessageDialog( frame, "Unable to add student - " + pendingException.getMessage, "AppName", JOptionPane.ERROR_MESSAGE); System.exit(1); // or let 'em retry? } } }.execute(); } Untested, undoubtedly borken in many ways, ++caveat emptor--; (Also IMO needs refactoring into smaller methods/classes to tame indentation a bit) > All that I/O - could end up being a lengthy process, ergo, a candidate to move > off the EDT. and it might be a good idea to check if it actually succeeded. According to the API PrintWriter.println does not throw any IOException if it fails. I'll leave it as an exercise for the OP to figure out how to handle this eventuality. SignatureNigel Wade, System Administrator, Space Plasma Physics Group, University of Leicester, Leicester, LE1 7RH, UK E-mail : nmw@ion.le.ac.uk Phone : +44 (0)116 2523548, Fax : +44 (0)116 2523555 Thanks red, I see that I had the code somewhat reveresed. It's alot clearer now how to use the try statement. Art Cummings >> My apologies, the code for the throw was assumed. I've included it here. >> [quoted text clipped - 39 lines] > > Untested, caveat emptor. > Good evening all, My evening is better when I do not need to chase after multi-posters asking them to 'kindly refrain from multi-posting in future'. (X-post to c.l.j.g./h., w/ f-u to c.l.j.h. only) -- Andrew T. my apologies, any suggestions on the code problem? >> Good evening all, > [quoted text clipped - 6 lines] > -- > Andrew T. >my apologies, Sure (I'll take that to read "it won't happen again" which is all that interests me). >any suggestions on the code problem? Roedy and Eric have offered some useful advice if you understand how to use it - you might research their suggestions further. I also recommend posting SSCCE code, as it helps people to see the exact problem, and avoids the need (largely) to provide later snippets of code. You can find more info. on the SSCCE here. <http://www.physci.org/codes/sscce.html> Another thing I recommend is to 'do as the locals do' and post 'in-line with trimming' as myself, Eric and Roedy have done, rather than 'top-post' replies. SignatureAndrew Thompson http://www.physci.org/ Thanks Andrew I've read the sscce doc and will comply in future post. Art Cummings >>my apologies, > [quoted text clipped - 17 lines] > and post 'in-line with trimming' as myself, Eric and > Roedy have done, rather than 'top-post' replies. On Thu, 29 Nov 2007 22:29:34 -0500, "Art Cummings" <aikiart7@gmail.com> wrote, quoted or indirectly quoted someone who said : >try >{ String name; >} catch (IOException x) the pattern is try { code that does IO . } catch ( IOExeception e ) { Code to deal with the IO screwing up. } see http://mindprod.com/jgloss/exception.html SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com Thanks Roedy, I'm starting to understand how to use try. Art Cummings > On Thu, 29 Nov 2007 22:29:34 -0500, "Art Cummings" > <aikiart7@gmail.com> wrote, quoted or indirectly quoted someone who [quoted text clipped - 20 lines] > > see http://mindprod.com/jgloss/exception.html >Good evening all, > [quoted text clipped - 9 lines] >point, i'm stuck. Any insight about how to do this, is appreciated. This >is an introductory java class so. [snip code] If you want to understand exceptions further then you can read the Sun tutorial at: http://java.sun.com/docs/books/tutorial/essential/exceptions/ In general the Sun tutorials are worth looking at if there is a part of Java you do not understand. You could also try experimenting on your own with something like: public class ExceptionTest { public static void thisThrows() { // Just throw an exception throw new Exception("this process has failed because your " + "computer is full of instant mashed potato."); } public static void main(String[] args) { try { thisThrows(); System.out.println("We are here."); } catch (Exception ex) { System.out.println("Exception thrown: " + ex.getMessage()); } System.out.println("Finished."); } } Yes, I know that will not compile, getting it to compile is part of the learning process (yes, I used to be a teacher). For extra credits, predict whether or not the "We are here" message will be printed before you run the code. rossum Thanks Rossum, This was a good reference. Art Cummings >>Good evening all, >> [quoted text clipped - 52 lines] > > rossum Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
|
Reply to this Message
|
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2008 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.