Home > Articles > Programming > Windows Programming

Introduction to the .NET Framework Class Library

In this sample chapter, Lars Powers and Mike Snell introduce the class library that ships with the .NET Framework. Examine its organization, and look at exactly how the classes operate as a reusable layer of functional building blocks for .NET developers.
This sample chapter is excerpted from chapter 4 of Visual Basic Programmer's Guide to the .NET Framework Class Library, by Lars Powers and Mike Snell.
This chapter is from the book


  • Introducing the Framework Class Library
  • Enhancing Developer Productivity
  • The Elements of a Namespace
  • Programming with the Framework Class Library

The Framework Class Library is a vast tapestry; it will take a while before you are familiar enough with it to immediately identify its possible uses in a given situation. This chapter will introduce you to the class library that ships with the .NET Framework. We will examine its organization, and look at exactly how the classes operate as a reusable layer of functional building blocks for .NET developers. You should walk away from this chapter understanding, in principle, what position in the larger .NET initiative that the Framework Class Library holds, and how it is really designed with the end developer in mind. You should also be primed and ready to look at actual code examples in the chapters that follow in Part II, "Working with the .NET Namespaces," of this book.

This chapter will specifically

  • Describe the organization of the class library namespaces.

  • Illustrate how the class library implements the core concepts of classes, enumerations, delegates, interfaces, and structures.

  • Identify the key productivity enhancements offered by programming against the class library.

So, before getting in to the actual makeup of the .NET base classes, we will examine a few basic aspects of the namespaces that constitute the class library.

Introducing the Framework Class Library

As you have probably figured out from its name, the class library is merely a collection of classes and related structures that can be leveraged as base building blocks for application development. As such, it is safe to think of this collection of classes as an API: They are a boundary interface between our applications and the operating system. This concept, of course, is really nothing new to Visual Basic developers: the ADO library, the Win32 API, the COM+ services library—all of these constructs have allowed us to reference and use pre-existing code in our applications. The class library is a massive library of pre-existing code that you can use as a foundation for your application features.


Referencing pre-existing libraries of code has traditionally been pretty easy with Visual Basic. One of the main issues, however, was that many times these code libraries weren't initially consumable by Visual Basic developers. If you were a C++ programmer, the world was open to you in terms of functionality. VB programmers had to wait for Microsoft or some other entity to make a wrapper or interface available that we could use from VB. Documentation also tended to be a problem.

Organization—The Namespace Hierarchy

The primary units of organization for the class library are namespaces. A namespace is just a bucket for functionality: It describes a grouping of like-focused classes and constructs. You can liken the concept of a namespace to that of a file system folder—they both attempt to implement organization across objects with parent and child relationships. Just as a folder can contain other folders and actual documents, a namespace can contain other namespaces or actual classes, delegates, and so on.

All namespaces stem from a common root: the System namespace. The System namespace is the one and only common root for all other namespaces.

The System namespace, for instance, contains the actual structures that define the common data types used in .NET such as Boolean, DateTime, and Int32. It also contains the most important data type of all, Object, which is the base object inherited by all other .NET objects.

Walking the Tree

The first level of children namespaces under the System namespace represents the high-level functionality groupings exposed by the API. Table 4.1 shows these high-level namespaces, with a brief description of their focus. Remember that each one of these high-level namespaces can (and likely will) have other children namespaces that further decompose and organize the functionality and focus of the parent namespace. A good example of this is the System.XML

namespace, which parents the System.XML.Schema, the System.XML.Serialization, the System.XML.XPath, and the System.XML.XSL namespaces.

TABLE 4.1 Primary Namespaces Under the System Root




Source code document structure and manipulation (including compilation).


Collections of objects including arrays, hash tables, and dictionaries.


Runtime and design-time behavior of components and controls.


Configuration settings management for the Framework.


Data access and management (essentially defines the ADO.NET technology).


Application debugging and execution tracing. Also included in this namespace are classes related to event log manipulation and performance monitoring.


Access to the Active Directory.


Graphics and drawing, including printing.


COM interactions and settings.


Definition of culture-specific settings.


Synchronous and asynchronous access to files and streams.


Access to WMI functionality.


Message creation and transmission in addition to management of message queues.


Network communications and protocols.


Examination and on-the-fly creation of types, methods, and fields.


Management of culture-specific resources.


Access to low-level runtime functions, including compilation and interop services.


General runtime security including policies, permissions, and credential resolution.


Creation and installation of Windows services.


Conversion and formatting of text.


Explicit thread creation and management.


Server-based timers.


Browser/server communication over HTTP.


Form-based Windows creation.


XML processing.

You should know that the Framework Class Library can be extended, but that the system root namespace will always contain classes that are universally useful to applications. Companies may introduce their own libraries that will co-exist with the System namespace and that will, in fact, operate under their own root namespace. Microsoft, for instance, has already shown us an example of this by including several language-focused namespaces under a root Microsoft namespace. Thus, we have Microsoft.Csharp, Microsoft.VisualBasic, and so on.

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.


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.


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.


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.


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


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


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.


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.


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