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.NET Framework Class Library Overview

The .NET Framework includes classes, interfaces, and value types that expedite and optimize the development process and provide access to system functionality. To facilitate interoperability between languages, most .NET Framework types are CLS-compliant and can therefore be used from any programming language whose compiler conforms to the common language specification (CLS).

The .NET Framework types are the foundation on which .NET applications, components, and controls are built. The .NET Framework includes types that perform the following functions:

  • Represent base data types and exceptions.

  • Encapsulate data structures.

  • Perform I/O.

  • Access information about loaded types.

  • Invoke .NET Framework security checks.

  • Provide data access, rich client-side GUI, and server-controlled, client-side GUI.

The .NET Framework provides a rich set of interfaces, as well as abstract and concrete (non-abstract) classes. You can use the concrete classes as is or, in many cases, derive your own classes from them. To use the functionality of an interface, you can either create a class that implements the interface or derive a class from one of the .NET Framework classes that implements the interface.

.NET Framework types use a dot syntax naming scheme that connotes a hierarchy. This technique groups related types into namespaces so they can be searched and referenced more easily. The first part of the full name — up to the rightmost dot — is the namespace name. The last part of the name is the type name. For example, System.Collections.ArrayList represents the ArrayList type, which belongs to the System.Collections namespace. The types in System.Collections can be used to manipulate collections of objects.

This naming scheme makes it easy for library developers extending the .NET Framework to create hierarchical groups of types and name them in a consistent, informative manner. It also allows types to be unambiguously identified by their full name (that is, by their namespace and type name), which prevents type name collisions. It is expected that library developers will use the following guideline when creating names for their namespaces:

CompanyName.TechnologyName

For example, the namespace Microsoft.Word conforms to this guideline.

The use of naming patterns to group related types into namespaces is a very useful way to build and document class libraries. However, this naming scheme has no effect on visibility, member access, inheritance, security, or binding. A namespace can be partitioned across multiple assemblies and a single assembly can contain types from multiple namespaces. The assembly provides the formal structure for versioning, deployment, security, loading, and visibility in the common language runtime.

For more information on namespaces and type names, see Common Type System.

The System namespace is the root namespace for fundamental types in the .NET Framework. This namespace includes classes that represent the base data types used by all applications: Object (the root of the inheritance hierarchy), Byte, Char, Array, Int32, String, and so on. Many of these types correspond to the primitive data types that your programming language uses. When you write code using .NET Framework types, you can use your language's corresponding keyword when a .NET Framework base data type is expected.

The following table lists the base types that the .NET Framework supplies, briefly describes each type, and indicates the corresponding type in Visual Basic, C#, C++, and JScript.

Category

Class name

Description

Visual Basic data type

C# data type

C++ data type

JScript data type

Integer

Byte

An 8-bit unsigned integer.

Byte

byte

unsigned char

Byte

   

SByte

An 8-bit signed integer.

Not CLS-compliant.

SByte

sbyte

char

-or-

signed char

SByte

   

Int16

A 16-bit signed integer.

Short

short

short

short

   

Int32

A 32-bit signed integer.

Integer

int

int

-or-

long

int

   

Int64

A 64-bit signed integer.

Long

long

__int64

long

   

UInt16

A 16-bit unsigned integer.

Not CLS-compliant.

UShort

ushort

unsigned short

UInt16

   

UInt32

A 32-bit unsigned integer.

Not CLS-compliant.

UInteger

uint

unsigned int

-or-

unsigned long

UInt32

   

UInt64

A 64-bit unsigned integer.

Not CLS-compliant.

ULong

ulong

unsigned __int64

UInt64

Floating point

Single

A single-precision (32-bit) floating-point number.

Single

float

float

float

   

Double

A double-precision (64-bit) floating-point number.

Double

double

double

double

Logical

Boolean

A Boolean value (true or false).

Boolean

bool

bool

bool

Other

Char

A Unicode (16-bit) character.

Char

char

wchar_t

char

   

Decimal

A decimal (128-bit) value.

Decimal

decimal

Decimal

Decimal

   

IntPtr

A signed integer whose size depends on the underlying platform (a 32-bit value on a 32-bit platform and a 64-bit value on a 64-bit platform).

IntPtr

No built-in type.

IntPtr

No built-in type.

IntPtr

No built-in type.

IntPtr

   

UIntPtr

An unsigned integer whose size depends on the underlying platform (a 32- bit value on a 32-bit platform and a 64-bit value on a 64-bit platform).

Not CLS-compliant.

UIntPtr

No built-in type.

UIntPtr

No built-in type.

UIntPtr

No built-in type.

UIntPtr

Class objects

Object

The root of the object hierarchy.

Object

object

Object*

Object

   

String

An immutable, fixed-length string of Unicode characters.

String

string

String*

String

In addition to the base data types, the System namespace contains over 100 classes, ranging from classes that handle exceptions to classes that deal with core runtime concepts, such as application domains and the garbage collector. The System namespace also contains many second-level namespaces.

For more information about namespaces, browse the .NET Framework Class Library reference. The reference documentation provides a brief overview of each namespace as well as a formal description of each type and its members.

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