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Handling Exceptions

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This chapter is from the book

Practice Questions

Question 1

You have created the following code segment:

Try
  ' Write code to allocate some 
resources Finally ' Write code to Dispose all allocated
resources End Try

Which of the following will result from compiling this code, assuming all other code for your form works properly?

  1. The code will generate an error because it lacks a Catch block.

  2. The code will generate an error because it lacks a Throw statement.

  3. The code will generate an error because the Finally block does not follow the End Try statement.

  4. The code will compile without an error.

Answer D is correct. The code will compile properly because it includes both a Try and a Finally block. Answer A is incorrect because a Try block must have either one or more Catch blocks or a Finally block (or both). Answer B is incorrect because the Throw statement is used to explicitly raise an error and is not required. Answer C is incorrect because the Finally block must follow the Try and Catch blocks but remain within the defined Try block terminated by the End Try statement.

Question 2

You have created a code segment that includes several MessageBox statements that detail the flow of its execution. The program has the following code:

Try
  Dim num As Integer = 100
  dim den as Integer = 0
  MessageBox.Show("Message1")
  Try
    Dim res As Integer = num / den
    MessageBox.Show("Message2")
  Catch ae As ArithmeticException
    MessageBox.Show("Message3")
  End Try
Catch dbze As DivideByZeroException
  MessageBox.Show("Message4")
Finally
  MessageBox.Show("Message5")
End Try

Which of the following is the order of messages that are generated when you run this code?

  1. Message1

    Message2

    Message3

    Message4

  2. Message5

    Message1

    Message3

    Message5

  3. Message1

    Message4

    Message5

    Message1

  4. Message2

    Message4

    Message5

Answer B is correct. The code will generate Message1 before entering the Try block, the attempted division by zero encountered by the Catch as ArithmeticException block will generate Message3, and the Finally block of code will generate Message5. Answers A and C are incorrect because they assume that all Catch blocks will be evaluated, rather than only the first matching exception Catch block. Answer D is incorrect because it fails to catch the first matching exception and instead includes the generation of Message2, which never occurs due to the raising of the division-by-zero error just before, and the generation of Message4, which never occurs because it falls after another matching Catch statement.

Question 3

You are designing a complex membership information form and want to provide a user-friendly interface while also notifying users when invalid information has been input. Which control should you use to display information about validation failures?

  1. ToolTip

  2. Label

  3. LinkLabel

  4. ErrorProvider

Answer D is correct. The ErrorProvider component provides a user-friendly notification for field validation, showing a small warning icon and displaying a ToolTip detailing the validation failure when the cursor is hovered over this icon. Answers A, B, and C are all incorrect.

Question 4

How should you arrange Catch blocks?

  1. Only one Catch block for each Try code block, located after the Try code block but before the End Try statement.

  2. Several Catch blocks within one Try code block, arranged starting with Exception and ending with the most specific exception.

  3. Several Catch blocks within one Try code block, arranged starting with the most specific exception and ending with Exception.

  4. Catch blocks should be used only when a Finally block is not used.

Answer C is correct. One or more Catch blocks may be used with a Try code block, arranged in order from the most specific exception to the most general because the first match will be used for evaluation. Answer A is incorrect because you may associate more than one Catch block with a Try block. Answer B is incorrect because it specifies a reversed order, starting with Exception. Nothing would ever be evaluated past the first Catch block, because Exception includes all other more-specific exceptions. Answer D is incorrect because Catch and Finally blocks may both be used if desired.

Question 5

You have designed a logon form with two TextBox controls named txtUserName and txtpassword. You want to ensure that the user can only enter lowercase characters in the controls. Which of the following solutions will fulfill this requirement using the simplest method?

  1. Program the KeyPress event of the form to convert uppercase letters to lowercase letters.

  2. Create a single event handler that is attached to the KeyPress event of the form. Program this event handler to convert the uppercase letters to lowercase.

  3. Set the CharacterCasing property of the controls to Lower.

  4. Use the CharacterCasing method of the controls to convert the letters to lowercase.

Answer C is correct. The simplest method to accomplish this requirement is to set the CharacterCasing property of the two controllers to Lower so that all input characters will be forced to lowercase. Answers A and B could be used to accomplish this task, but this would not be the simplest solution available. Answer d is incorrect because there is no CharacterCasing method for TextBox controls. CharacterCasing is a property that accepts values of Normal, Lower, or Upper.

Question 6

Which of the following events will fire when the Insert key is pressed? [Select all correct answers.]

  1. KeyDown

  2. KeyPress

  3. KeyUp

Answers A and C are correct. When control and cursor navigation keys are pressed, only the KeyDown and KeyUp events are fired. Answer B is incorrect because the KeyPress event occurs only when a keyboard key generates a character.

Question 7

You have a TextBox control and a help button that the user can click to get help on allowable values. You validate the data entered by the user in the TextBox control, and if the user enters an invalid value you set the focus back in the control using the Cancel property of CancelEventArgs. A user reports that once he enters invalid data in the text box, he cannot click the help button. What should you do to correct the problem?

  1. Set the CausesValidation property of the text box to False

  2. Set the CausesValidation property of the text box to True

  3. Set the CausesValidation property of the help button to False

  4. Set the CausesValidation property of the help button to True

Answer C is correct. By setting the CausesValidation property of the help button to False, you allow it to act without first firing the Validating event in the text box, which would return the focus to the text box. Answers A and B are incorrect because changing the CausesValidation property of the text box will not affect the ability of the help button to be selected. Answer D is incorrect because setting the CausesValidation property of the help button to True (the default value) would result in the same problem experienced by the user.

Question 8

Your program contains the following code (line numbers are for reference only):

1
2 Try
3
4 Catch ex As Exception
5
6 Finally
7
8 End Try

At which lines could you insert a Throw statement to explicitly raise an exception? [Select all correct answers.]

  1. Line 1

  2. Line 3

  3. Line 5

  4. Line 7

Answers A, B, and C are correct. You can use a Throw block to raise a custom error whenever there isn't an unhandled error already pending. You should not use the Throw statement within the Finally block to explicitly raise a custom error because it is possible to have unhandled errors already when in the Finally block of code. Therefore, answer D is incorrect.

Question 9

You have an order-entry form. When an exception occurs, you want to get information about the sequence of method calls and the line number in the method where the exception occurs. Which property of your custom exception class that derives from the ApplicationException class should be used?

  1. HelpLink

  2. InnerException

  3. Message

  4. StackTrace

Answer D is correct. The StackTrace property of the Exception class provides information about the method call sequence and the line number where the exception occurred. Answer A is incorrect because the HelpLink property specifies the URL for an associated help file. Answer B is incorrect because the InnerException property details an exception associated with the raised exception. Answer C is incorrect because the Message property is used to explain the error or offer possible corrective actions.

Question 10

You want to log events generated by exception-handling code within your application, which will run on standalone systems running Windows 98 and Windows 2000. Which of the four methods of logging is the best single solution able to fulfill this requirement?

  1. Using the Windows Event Log

  2. Using custom log files

  3. Using a database such as SQL Server 2000

  4. Using email notifications

Answer B is correct. The best solution in this scenario is to use a local custom log file. Answer A is incorrect because some of the systems are running Windows 98, which does not support logging using the Event Log. Answers C and D are incorrect because standalone systems will not have network access to allow for the connection to a databases or the transmission of SMTP messages.

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