Miscellaneous Topics Announcements, Exceptions, and Dialogs

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Miscellaneous TopicsAnnouncements, Exceptions,
and Dialogs

• November 14, 2005

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Test Wednesday

• The second test is Wednesday!!
• Closed book and notes.
• No calculators.
• 5-6 Questions.
• Includes Applets, GUIs, Loops, and Arrays.

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Project 5

• How is it going? Are you able to write a list of
  your items out to a file? Can you read them back
  in?
• This weeks lab deals a bit with GUIs and
  probably will provide you with some help in
  building your GUI for this project.

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Basic Concept

• Build a panel which displays and controls one
  item in your inventory.
• Once that is built and looks okay go ahead and
  create a bunch of them and add them to a layout.

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An Example from this Weeks Lab

• Stores information on an album
• Laid out as 4 portions, the albumInfo, the stock,
  the box containing the quantity to buy, and a
  button.

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Exceptions

• Java uses Exceptions to catch mistakes.
• Traditionally, we used to have to test error
  conditions ourselves using if statements.
• This worked but it was easy to overlook an item
  that needed to be tested.

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Try, Catch, Finally, and Throw

• In using the I/O in Java we have seen a try-catch
  block.
• try // some statements
• catch (Exception e)
• // handle the exception

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There is another clause

• try
• // a group of statements catch (Exception e)
  // The error handling code finally
• // Done at the end regardless of
• // whether an exception occurred // or not.

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There Are All Kinds Of Exceptions

• Exception
• RuntimeException
• ArithmeticException
• ArrayStoreException
• ClassCastException
• IllegalArgumentException
• NumberFormatException
• IllegalMonitorStateException
• IndexOutOfBoundsException
• ArrayIndexOutOfBoundsException
• StringIndexOutOfBoundsException
• NegativeArraySizeException
• NullPointerException
• SecurityException

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Making You Own Exceptions

• You can build your own exceptions in Java to
  signal when bad things happen.
• To initiate or start the exception you use a
  throw statement.
• throw new Exception(Something is wrong!)

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Catching Multiple Exceptions

• Sometimes a block of code in a try-catch clause
  will throw more than one type of exception.
• Options
• Catch only an Exception (all Exceptions are
  descendents of the Exception class).
• Catch each type of exception thrown indepently
  (definitely preferable)

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Arranging the Catch Clauses

• The Catch clauses should be arranged from most
  specific to most general.
• If you are going to catch an Exception it should
  be the last one in the sequence.

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Example

• try // Some code block catch
  (NumberFormatException e) // Handle a
  number format catch (IllegalArgumentException
  e) // Handle an illegal argument catch
  (Exception e) // Handle any exception

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Example (BAD!)

• try // Some code block catch (Exception e)
  // This will catch all exceptions the
  // following two can never be reached. catch
  (IllegalArgumentException e) // Handle an
  illegal argument catch (NumberFormatException
  e) // Handle a NumberFormat exception

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Dialogs
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Creating (and using) a Dialog Box

• In Swing it is relatively easy to create a number
  of dialog boxes.
• They are created through a number of classes.
• Can involve input values as well as being
  informational.

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JOptionPane.showMessagePane

• Can be used to demonstrate a simple message.
• Does not allow any special input.
• Has the following call pattern
• JOptionPane.showMessageDialog(window,
• "This is an Informational
  Message",
• "Demo Dialog -- Info
  Message",
• JOptionPane.INFORMATION_MESS
  AGE)

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Dialog Box Appearance
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JOptionPane.showOptionDialog

• Used when a dialog has more than one option (yes,
  no, cancel?)
• returns an int indicating which button was
  pressed.
• Can customize the buttons to read whatever you
  wish

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Sample Code Dialog

• int resultString buttonLabels new String
  "Yes", "Almost"result JOptionPane.showOption
  Dialog(window, "Are you ready
  for the test Wednesday?", "Question
  Dialog", JOptionPane.YES_NO_OPTION, JOptionPan
  e.QUESTION_MESSAGE, null, buttonLabels, butt
  onLabels1)

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Dialog From Screen
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JOptionPane.showInputDialog

• Used to input a string or one of a number of
  choices.
• Returns the string.
• Can be closed without returning a string. (the x
  in the corner).

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Sample Code Type in Text...

• String s
• s (String) JOptionPane.showInputDialog(window,
• "Input your name ",
• "Input Dialog",
• JOptionPane.PLAIN_MESSAGE,
• null,
• null,
• null)

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Dialog Appearance
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Sample Code Pick From List

• String s
• String options new String "A", "B", "C",
  "D", "F"
• s (String) JOptionPane.showInputDialog(window,
• "Grade you
  expect ",
• "Guess Your
  Grade",
• 
  JOptionPane.PLAIN_MESSAGE,
• null,
• options,
• "A")

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Dialog Appearance
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Adding a File Chooser

• Many applications allow you to have a file
  chooser to pick a file rather than typing in a
  name.
• Simplest form in Java is the JFileChooser
• The value returned is which button was pressed
  (OK? or Cancel?)

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Sample Code

• public void showFileChooser( )
• JFileChooser chooser new JFileChooser()
• int option
• option chooser.showOpenDialog(window)
• if (option JFileChooser.APPROVE_OPTION)
  
• System.out.println("You chose "
  chooser.getSelectedFile() " from the
  list")
• else
• System.out.println("You Canceled out of
  the Dialog")

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The Dialog
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Can Alter What is Selected

• While the example given didn't do it we can set
  up a file selection mode that only gives files of
  a certain type.
• This is all the time I plan on spending on
  Dialogs. There are a lot of things that can be
  done with them but we have the basics for now