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Introduction to the .NET Framework Class Library

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, the .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.

Naming Conventions

.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 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.

System Namespace

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 some of the value types the .NET Framework supplies, briefly describes each type, and indicates the corresponding type in Visual Basic, C#, and the Managed Extensions for C++. The table also includes entries for the Object and String classes, for which many languages have corresponding keywords.

Category Class name Description Visual Basic data type C# data type Managed Extensions for C++ data type JScript data type
Integer Byte An 8-bit unsigned integer. Byte byte char Byte
    SByte An 8-bit signed integer.

Not CLS-compliant.

SByte

No built-in type.

sbyte 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.

UInt16

No built-in type.

ushort unsigned short UInt16
    UInt32 A 32-bit unsigned integer.

Not CLS-compliant.

UInt32

No built-in type.

uint unsigned int

-or-

unsigned long

UInt32
    UInt64 A 64-bit unsigned integer.

Not CLS-compliant.

UInt64

No built-in type.

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 96-bit decimal 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 almost 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 Reference. The reference documentation provides a brief overview of each namespace as well as a formal description of each type and its members.

See Also

Common Type System | .NET Framework Reference | Inside the .NET Framework

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