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