Namespaces and Class Libraries

Namespaces

All user-defined classes and structures, as a rule, don’t exist in a vacuum, but are enclosed in special containers called namespaces. The Program class generated by default upon the creation of a new .NET project already resides in a namespace. The name of this namespace is usually the same as the name of the project:

namespace MyFirstProject
{
	class Program
	{
		static void Main(string[] args)
		{
		}
	}
}

Defining a namespace

A namespace is defined using the namespace keyword, followed by the name. In the example above, the full name of the Program class is MyFirstProject.Program.

The Program class sees all other classes defined in the same namespace:

namespace MyFirstProject
{
    class Program
    {
        static void Main()
        {
            Employee employee = new Employee();
        }
    }

    class Employee
    {
    }
}

Importing namespaces

To use classes from other namespaces, the others must be imported with the using directive:

using System;

The above statement lets us use all classes from the System namespace, including the Console class that’s used to print to the console:

Console.WriteLine("Hello World!");

If we opt not to bring the System namespace, we have to use the full name of the class to access its members:

System.Console.WriteLine("Hello World!");

Consider the following code. Inspect it and make it run.