C# FAQ: What is a namespace
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What is a namespace?
A namespace is a method of organizing a group of assemblies, classes, or types. A namespace acts as a container—like a disk folder—for classes organized into groups usually based on functionality. C# namespace syntax allows namespaces to be nested.
For instance, to access the built-in input-output (I/O) classes and members, use the System.IO namespace. Or, to access Web-related classes and members, use the System.Web namespace.
All C# programs should call the System namespace—the father of all .NET Framework namespaces.
A namespace is similar to a Java package. However, whereas Java package names dictate the source files directory structure, C# namespaces dictate only the logical structure.
The C++ namespace syntax is similar to the C# syntax.
Using namespaces
Namespaces are referenced by C# applications by using the using keyword. For instance, the following example references the System namespace:
using System;
Unlike the Java language, an individual class cannot be referenced with the using keyword. A compilation error would result.
Referencing System namespace gives access to the Console class which can be used to perform console I/O. For instance, the following source code writes a line of text to the Console:
Console.WriteLine ("A console message.");
Aliases
Although the using keyword cannot be used with individual class names, aliases can! Read how to create a namespace alias.
Commonly used namespaces
The following is list of some important and frequently used .NET namespaces:
-
System.Collections -
System.Data -
System.Diagnostics -
System.Drawing -
System.IO -
System.Net -
System.Reflection -
System.Runtime -
System.Security -
System.Threading -
System.Web -
System.Windows.Forms -
System.Xml
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A C# namespace is the equivalent of a Java language package.
See also
- How use an alias for a class or namespace?
- What is a namespace?