.NET is not a collection of languages as somebody pointed out ...!!!!!!
It is just a platform on top of which other languages operates.
The Microsoft .NET Framework allows developers to leverage technologies more than any
earlier Microsoft development platform did. Specifically, the .NET Framework really delivers
on code reuse, code specialization, resource management, multilanguage development,
security, deployment, and administration. While designing this new platform, Microsoft also
felt it was necessary to improve on some of the deficiencies of the current Windows platform.
The following list gives you just a small sampling of what the CLR and the FCL provide:
§ Consistent programming model Unlike today, where some operating system
facilities are accessed via dynamic-link library (DLL) functions and other facilities are
accessed via COM objects, all application services are offered via a common objectoriented
programming model.
§ Simplified programming model The CLR seeks to greatly simplify the plumbing and
arcane constructs required by Win32 and COM. Specifically, the CLR now frees the
developer from having to understand any of the following concepts: the registry, globally
unique identifiers (GUIDs), IUnknown, AddRef, Release , HRESULTs, and so on. The
CLR doesn’t just abstract these concepts away from the developer; these concepts
simply don’t exist, in any form, in the CLR. Of course, if you want to write a .NET
Framework application that interoperates with existing, non-.NET code, you must still be
aware of these concepts.
§ Run once, run always All Windows developers are familiar with “DLL hell” versioning
problems. This situation occurs when components being installed for a new application
overwrite components of an old application, causing the old application to exhibit
strange behavior or stop functioning altogether. The architecture of the .NET
Framework now isolates application components so that an application always loads the
components that it was built and tested with. If the application runs after installation,
then the application should always run. This slams shut the gates of “DLL hell.”
§ Simplified deployment Today, Windows applications are incredibly difficult to set up
and deploy. Several files, registry settings, and shortcuts usually need to be created. In
addition, completely uninstalling an application is nearly impossible. With Windows
2000, Microsoft introduced a new installation engine that helps with all these issues, but
it’s still possible that a company authoring a Microsoft installer package might fail to do
everything correctly. The .NET Framework seeks to banish these issues into history.
The .NET Framework components (known simply as types) are not referenced by the
registry. In fact, installing most .NET Framework applications requires no more than
copying the files to a directory and adding a shortcut to the Start menu, desktop, or
Quick Launch bar. Uninstalling the application is as simple as deleting the files.
§ Wide platform reach When compiling source code for the .NET Framework, the
compilers produce common intermediate language (CIL) instead of the more traditional
CPU instructions. At run time, the CLR translates the CIL into native CPU instructions.
Because the translation to native CPU instructions is done at run time, the translation is
done for the host CPU. This means that you can deploy your .NET Framework
application on any machine that has an ECMA-compliant version of the CLR and FCL
running on it. These machines can be x86, IA64, Alpha, PowerPC, and so on. Users will
immediately appreciate the value of this broad execution if they ever change their
computing hardware or operating system.
§ Programming language integration COM allows different programming languages
to interoperate with one another. The .NET Framework allows languages to be
integrated with one another so that you can use types of another language as if they are
your own. For example, the CLR makes it possible to create a class in C++ that derives
from a class implemented in Visual Basic. The CLR allows this because it defines and
provides a Common Type System (CTS) that all programming languages that target the
CLR must use. The Common Language Specification (CLS) describes what compiler
implementers must do in order for their languages to integrate well with other
languages. Microsoft is itself providing several compilers that produce code targeting
the runtime: C++ with Managed Extensions, C#, Visual Basic .NET (which now
subsumes Visual Basic Scripting Edition, or VBScript, and Visual Basic for Applications,
or VBA), and JScript. In addition, companies other than Microsoft and academic
institutions are producing compilers for other languages that also target the CLR.
§ Simplified code reuse Using the mechanisms described earlier, you can create your
own classes that offer services to third-party applications. This makes it extremely
simple to reuse code and also creates a large market for component (type) vendors.
§ Automatic memory and management (garbage collection) Programming requires
great skill and discipline, especially when it comes to managing the use of resources
such as files, memory, screen space, network connections, database resources, and so
on. One of the most common bugs is neglecting to free one of these resources,
ultimately causing the application to perform improperly at some unpredictable time.
The CLR automatically tracks resource usage, guaranteeing that your application never
leaks resources. In fact, there is no way to explicitly “free” memory. In Chapter 19,
“Automatic Memory Management (Garbage Collection),” I explain exactly how garbage
collection works.
§ Type-safe verification The CLR can verify that all your code is type-safe. Type safety
ensures that allocated objects are always accessed in compatible ways. Hence, if a
method input parameter is declared as accepting a 4-byte value, the CLR will detect
and trap attempts to access the parameter as an 8-byte value. Similarly, if an object
occupies 10 bytes in memory, the application can’t coerce the object into a form that will
allow more than 10 bytes to be read. Type safety also means that execution flow will
transfer only to well-known locations (that is, method entry points). There is no way to
construct an arbitrary reference to a memory location and cause code at that location to
start executing. Together, these measures ensure type safety eliminating many
common programming errors and classic system attacks (for example, exploiting buffer
overruns).
§ Rich debugging support Because the CLR is used for many programming
languages, it is now much easier to implement portions of your application using the
language best suited to a particular task. The CLR fully supports debugging applications
that cross language boundaries.
§ Consistent method failure paradigm One of the most aggravating aspects of
Windows programming is the inconsistent style that functions use to report failures.
Some functions return Win32 status codes, some functions return HRESULTs, and
some functions throw exceptions. In the CLR, all failures are reported via exceptions—
period. Exceptions allow the developer to isolate the failure recovery code from the
code required to get the work done. This separation greatly simplifies writing, reading,
and maintaining code. In addition, exceptions work across module and programming
language boundaries. And, unlike status codes and HRESULTs, exceptions can’t be
ignored. The CLR also provides built-in stack-walking facilities, making it much easier to
locate any bugs and failures.
§ Security Traditional operating system security provides isolation and access control
based on user accounts. This model has proven useful, but at its core assumes that all
code is equally trustworthy. This assumption was justified when all code was installed
from physical media (for example, CD-ROM) or trusted corporate servers. But with the
increasing reliance on mobile code such as Web scripts, applications downloaded over
the Internet, and e-mail attachments, we need ways to control the behavior of
applications in a more code-centric manner. Code access security provides a means to
do this.
§ Interoperability Microsoft realizes that developers already have an enormous amount
of existing code and components. Rewriting all this code to take full advantage of the
.NET Framework platform would be a huge undertaking and would prevent the speedy
adoption of this platform. So the .NET Framework fully supports the ability for the
developer to access their existing COM components as well as call Win32 functions in
existing DLLs.
Users won’t directly appreciate the CLR and its capabilities, but they will certainly notice the
quality and features of applications that utilize the CLR. In addition, users and your
company’s bottom line will appreciate how the CLR allows applications to be developed and
deployed more rapidly and with less administration than Windows has ever allowed in the
past.