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Handling Exceptions

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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
}

Which of the following will result from compiling this code, assuming that 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 is placed immediately after the try block.

  4. The code will compile without an error.

Answer D is correct. The code will compile properly because a try block should be followed by either a catch block or a finally block. The code here includes both a try block followed by a finally block. Answer A is incorrect because a try block can be followed by 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 a finally block can be placed after a try block.

Question 2

What will be the output of the following code?

try
{
  int num = 100;
  int den = 0;
  try
  {
    MessageBox.Show("Message1");
    int res = num/den;
    MessageBox.Show("Message2");
  }
  catch(ArithmeticException ae)
  {
    MessageBox.Show("Message3");
  }
  MessageBox.Show("Message4");
}
  1. Message1
    Message4
  2. Message1
    Message2
    Message3
    Message4
  3. Message1
    Message3
    Message4
  4. Message1
    Message3
    Message2
    Message4

Answer C is correct. This code first displays Message1 and executes the next line to perform the division. Because the denominator is 0, a DivideByZeroException is raised. Because the code that raises the exception is enclosed in a try block, the program searches for a matching catch block associated with that try block. The code finds a matching catch block with ArithmeticException (that is a base class for the DivideByZeroException exception), which can handle the exception. Therefore, it executes the catch block and displays Message3. After executing the catch block, control comes to the next line after the catch block, and the program displays Message4. Answer A is not correct because the program is capable of locating a catch block that can catch DivideByZeroException. Answer B is not correct because when an exception is raised, the code first searches for the catch block that can handle the exception. Answer D is not correct because after the code in the catch block is executed, control is transferred to the next line after the catch block.

Question 3

How should you arrange catch blocks?

  1. Only one catch block for each try block.

  2. Several catch blocks for a try block, arranged in order starting with Exception and ending with the most specific exception.

  3. Several catch blocks within one try block, arranged starting with the most specific exception and ending with Exception.

  4. The catch blocks should be used only when a finally block is not used.

Answer C is correct. One or more catch blocks can be used with a try block, arranged in order from the most specific exception to the most general; the first matching catch block catches the exception. Answer A is incorrect because you can associate more than one catch block with a try block. Answer B is incorrect because it specifies a reversed order, starting with Exception class. The compiler generates an error if the catch blocks are not arranged from specific to generic types. Answer D is incorrect because catch and finally blocks can both be used together, if desired.

Question 4

You have designed a logon form with two TextBox controls named txtUserName and txtpassword. You want to ensure that the user can enter only 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 TextBox controls 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 ones.

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

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

Answer C is correct. The simplest method to accomplish this requirement is to set the CharacterCasing property of the two TextBox controls 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 5

You are creating an order-tracking application using a Visual C# .NET Windows application. When you are unable to track a particular order number entered by the user, you need to raise an exception. Which of the following options will help you to raise an exception?

  1. try block

  2. catch block

  3. finally block

  4. throw statement

Answer D is correct. The throw statement is used to raise an exception. Answer A is not correct because the try block is used to place code that can raise exceptions. Answer B is not correct because the catch block is used to catch and handle exceptions. Answer C is not correct because the finally block is used to insert code that always needs to be executed, such as resource-cleanup code.

Question 6

Which of the following events will fire when the Insert key is pressed? (Choose all correct answers.)

  1. KeyDown

  2. KeyPress

  3. KeyUp

  4. Move

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 press to get help on allowable values. You validate the data entered by the user in the TextBox control. If the user enters an invalid value, you set the focus back in the control using the Cancel property of the 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 TextBox, which would return the focus to the TextBox. Answers A and B are incorrect because changing the CausesValidation property of the textbox will not affect the capability 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

You are designing a Windows Form that enables you to add a new product to the product catalog of your company. You need to validate the controls as the user enters the data. If incorrect data is entered in the field, you should set the focus back to the control and ask the user to enter the correct data. Which of the following events will you use to validate user input?

  1. LostFocus

  2. Validating

  3. Leave

  4. Validated

Answer B is correct. The Validating event is the ideal place to store the validating logic for a field. Answers A and C are not correct because these events are not intended for validation. Properties such as CausesValidation and Cancel, which provide important roles in control validation, affect only the Validating and Validated events. Answer D is not correct because the Validated event is fired after the validation is performed.

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 method of the Exception class provides information about the method call sequence and 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. Windows event log

  2. Custom log files

  3. Databases such as SQL Server 2000

  4. 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 connection to databases or transmission of SMTP messages.

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