page 7 Programming C# John Osborn signed me to O'Reilly, for which I will forever be in his debt...

Ludzie pragną czasami się rozstawać, żeby móc tęsknić, czekać i cieszyć się z powrotem.

Valerie Quercia, Brian McDonald, Jeff Holcomb, Claire Cloutier, and Tatiana Diaz helped make this book better than what I'd written. Rob Romano created a number of the illustrations and improved the others.
Al Stevens and Eric Gunnerson reviewed the manuscript and saved me from a series of embarrassing errors and omissions. I am deeply grateful.
Part I: The C# Language
Chapter 1. C# and the .NET Framework
The goal of C# is to provide a simple, safe, modern, object-oriented, Internet-centric, high-performance language for .NET development. C# is a new language, but it draws on the lessons learned over the past three decades. In much the way that you can see in young children the features and personalities of their parents and grandparents, you can easily see in C# the influence of Java, C++, Visual Basic (VB), and other languages.
The focus of this book is the C# language and its use as a tool for programming on the .NET
platform. In my primers on C++,[1] I advocate learning the language first, without regard to Windows or Unix programming. With C# that approach would be pointless. You learn C#
specifically to create .NET applications; pretending otherwise would miss the point of the language.
Thus, this book does not consider C# in a vacuum but places the language firmly in the context of Microsoft's .NET platform and in the development of desktop and Internet applications.
[1] See Sams Teach Yourself C++ in 21 Days, also by Jesse Liberty.
This chapter introduces both the C# language and the .NET platform, including the .NET
Framework.
1.1 The .NET Platform
When Microsoft announced C# in July 2000, its unveiling was part of a much larger event: the announcement of the .NET platform. The .NET platform is, in essence, a new development framework that provides a fresh application programming interface (API) to the services and APIs of classic Windows operating systems, especially Windows 2000, while bringing together a number of disparate technologies that emerged from Microsoft during the late 1990s. Among the latter are COM+ component services, the ASP web development framework, a commitment to XML and object-oriented design, support for new web services protocols such as SOAP, WSDL, and UDDI, and a focus on the Internet, all integrated within the DNA architecture.
Microsoft says it is devoting 80% of its research and development budget to .NET and its associated technologies. The results of this commitment to date are impressive. For one thing, the scope of
.NET is huge. The platform consists of four separate product groups:
• A set of languages, including C# and Visual Basic .NET; a set of development tools, including Visual Studio .NET; a comprehensive class library for building web services and web and Windows applications; as well as the Common Language Runtime (CLR) to execute objects built within this framework.
• A set of .NET Enterprise Servers, formerly known as SQL Server 2000, Exchange 2000, BizTalk 2000, and so on, that provide specialized functionality for relational data storage, email, B2B commerce, etc.

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• An offering of commercial web services, recently announced as Project Hailstorm; for a fee, developers can use these services in building applications that require knowledge of user identity, etc.
• New .NET-enabled non-PC devices, from cell phones to game boxes.
1.2 The .NET Framework
Microsoft .NET supports not only language independence, but also language integration. This means that you can inherit from classes, catch exceptions, and take advantage of polymorphism across different languages. The .NET Framework makes this possible with a specification called the Common Type System (CTS) that all .NET components must obey. For example, everything in
.NET is an object of a specific class that derives from the root class called System.Object. The CTS supports the general concept of classes, interfaces, delegates (which support callbacks), reference types, and value types.
Additionally, .NET includes a Common Language Specification (CLS), which provides a series of basic rules that are required for language integration. The CLS determines the minimum requirements for being a .NET language. Compilers that conform to the CLS create objects that can interoperate with one another. The entire Framework Class Library (FCL) can be used by any language that conforms to the CLS.
The .NET Framework sits on top of the operating system, which can be any flavor of Windows,[2]
and consists of a number of components. Currently, the .NET Framework consists of:
[2] Because of the architecture of the CLR, the operating system can be potentially any flavor of Unix or another operating system altogether.
• Four official languages: C#, VB .NET, Managed C++, and JScript .NET
• The Common Language Runtime (CLR), an object-oriented platform for Windows and web development that all these languages share
• A number of related class libraries, collectively known as the Framework Class Library (FCL).
Figure 1-1 breaks down the .NET Framework into its system architectural components.
Figure 1-1. NET Framework architecture

The most important component of the .NET Framework is the CLR, which provides the environment in which programs are executed. The CLR includes a virtual machine, analogous in many ways to the Java virtual machine. At a high level, the CLR activates objects, performs page 9
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