Namespace (Namespace)

Namespace

Define the namespace

The definition of a namespace starts with the keyword namespace, followed by the name of the namespace, as follows:

namespace namespace_name
{
   // 代码声明
}

In order to call a function or variable that supports the namespace version, the name of the namespace is placed first, as follows:

namespace_name.item_name;

The following program demonstrates the use of namespaces:

using System;
namespace first_space
{
   class namespace_cl
   {
      public void func()
      {
         Console.WriteLine("Inside first_space");
      }
   }
}
namespace second_space
{
   class namespace_cl
   {
      public void func()
      {
         Console.WriteLine("Inside second_space");
      }
   }
}   
class TestClass
{
   static void Main(string[] args)
   {
      first_space.namespace_cl fc = new first_space.namespace_cl();
      second_space.namespace_cl sc = new second_space.namespace_cl();
      fc.func();
      sc.func();
      Console.ReadKey();
   }
}

When the above code is compiled and executed, it produces the following results:

Inside first_space
Inside second_space

The using keyword

The using keyword indicates that the program is using a name in a given namespace. F or example, we use the System namespace in our program, which defines the class Console. We can just write:

Console.WriteLine ("Hello there");

We can write a fully qualified name, as follows:

System.Console.WriteLine("Hello there");

You can also use the using namespace directive so that you don't have to add a namespace name to the front when you use it. T he instruction tells the compiler that subsequent code uses a name in the specified namespace. The following code delays the application of namespaces.

Let's use using using to specify to override the above example:

using System;
using first_space;
using second_space;

namespace first_space
{
   class abc
   {
      public void func()
      {
         Console.WriteLine("Inside first_space");
      }
   }
}
namespace second_space
{
   class efg
   {
      public void func()
      {
         Console.WriteLine("Inside second_space");
      }
   }
}   
class TestClass
{
   static void Main(string[] args)
   {
      abc fc = new abc();
      efg sc = new efg();
      fc.func();
      sc.func();
      Console.ReadKey();
   }
}

When the above code is compiled and executed, it produces the following results:

Inside first_space
Inside second_space

Nested namespaces

Namespaces can be nested, i.e. you can define another namespace within one namespace, as follows:

namespace namespace_name1 
{
   // 代码声明
   namespace namespace_name2 
   {
     // 代码声明
   }
}

You can use the point (.) operator to access members of nested namespaces, as follows:

using System;
using first_space;
using first_space.second_space;

namespace first_space
{
   class abc
   {
      public void func()
      {
         Console.WriteLine("Inside first_space");
      }
   }
   namespace second_space
   {
      class efg
      {
         public void func()
         {
            Console.WriteLine("Inside second_space");
         }
      }
   }   
}
 
class TestClass
{
   static void Main(string[] args)
   {
      abc fc = new abc();
      efg sc = new efg();
      fc.func();
      sc.func();
      Console.ReadKey();
   }
}

When the above code is compiled and executed, it produces the following results:

Inside first_space
Inside second_space