Home > Articles > Certification > Microsoft Certification

  • Print
  • + Share This
This chapter is from the book

Understanding Exceptions

An exception occurs when a program encounters any unexpected problems such as running out of memory or attempting to read from a file that no longer exists. These problems are not necessarily caused by programming errors but mainly occur due to violations of certain assumptions that are made about the execution environment.

When a program encounters an exception, its default behavior is to throw the exception, which generally translates to abruptly terminating the program after displaying an error message. This is not a characteristic of a robust application and does not make your program popular with users. Your program should be able to handle these exceptional situations and, if possible, gracefully recover from them. This is called exception handling. Proper use of exception handling can make programs robust and easy to develop and maintain. However, if you do not use exception handling properly, you might end up having a program that performs poorly, is harder to maintain, and may potentially mislead its users.

Step by Step 3.1 demonstrates how an exception may occur in a program. Later in this chapter I explain how to handle these exceptions.

STEP BY STEP 3.1 - Exceptions in Windows Applications

  1. Create a new C# Windows application project in the Visual Studio .NET Integrated Development Environment (IDE). Name the project 316C03.

  2. Add a new Windows form to the project. Name it StepByStep3_1.

  3. Place three TextBox controls (txtMiles, txtGallons, and txtEfficiency) and a Button control (btnCalculate) on the form and arrange them as shown in Figure 3.1. Add Label controls as necessary.

Figure 3.1Figure 3.1 The mileage efficiency calculator does not implement any error handling for the user interface.

  1. Add the following code to the Click event handler of btnCalculate:

    private void btnCalculate_Click(
      object sender, System.EventArgs e)
    {
      //this code has no error checking. If something
      //goes wrong at run time,
      //it will throw an exception
      decimal decMiles =
        Convert.ToDecimal(txtMiles.Text);
      decimal decGallons =
        Convert.ToDecimal(txtGallons.Text);
      decimal decEfficiency = decMiles/decGallons;
      txtEfficiency.Text =
        String.Format("{0:n}", decEfficiency);

    }

  2. Insert the Main() method to launch the form. Set the form as the startup object for the project.

  3. Run the project. Enter values for miles and gallons and click the Calculate button. The program calculates the mileage efficiency, as expected. Now enter the value 0 in the Gallons of Gas Used field and run the program. The program abruptly terminates after displaying an error message (see Figure 3.2).

Figure 3.2Figure 3.2 The development environment gives you a chance to analyze the problem when an exception occurs.

When you run the program created in Step by Step 3.1 from the IDE and the program throws an exception, the IDE gives you options to analyze the problem by debugging the program. In Step by Step 3.1, if you had instead run the program by launching the project's .exe file from Windows Explorer, the program would have terminated after displaying a message box with an error message and some debugging information (see Figure 3.3).

Figure 3.3Figure 3.3 When a program is executed outside the Visual Studio .NET environment, debugging information is displayed when an exception is thrown.

From the CLR's point of view, an exception is an object that encapsulates information about the problems that occur during program execution. The FCL provides two categories of exceptions:

  • ApplicationException—Represents exceptions thrown by the applications

  • SystemException—Represents exceptions thrown by the CLR

Both of these exception classes derive from the base class Exception, which implements the common functionality for exception handling. Neither the ApplicationException class nor the SystemException class adds any new functionality to the Exception class; they exist just to differentiate exceptions in applications from exceptions in the CLR. The classes derived from Exception share some important properties, as listed in Table 3.1

Table 3.1 Important Members of the Exception Class

Member

Type

Description

HelpLink

Property

Specifies the uniform resource locator (URL) of the help file associated with this exception.

InnerException

Property

Specifies an exception associated with this exception. This property is helpful when a series of exceptions are involved. Each new exception can preserve the information about the previous exception by storing it in the InnerException property.

Message

Property

Specifies textual information that indicates the reason for the error and provides possible resolutions.

Source

Property

Specifies the name of the application that causes the error.

StackTrace

Property

Specifies where an error has occurred. If the debugging information is available, the stack trace includes the name of the source file and the program line number.

TargetSite

Property

Represents the method that throws the current exception.


  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020