Classes and Namespaces in C#

Classes and Namespaces in C#

All C# programs are composed entirely of classes. Visual windows forms are a type of class, as we will see that all the program features we’ll write are composed of classes. Since everything is a class, the number of names of class objects can get to be pretty overwhelming. They have therefore been grouped into various functional libraries that you must specifically mention in order to use the functions in these libraries.

Under the covers these libraries are each individual DLLs. However, you need only refer to them by their base names using the using statement, and the functions in that library are available to you.

using System;

using System.Drawing;

using System.Collections;

Logically, each of these libraries represents a different namespace. Each namespace is a separate group of class and method names which the compiler will recognize after you declare that name space. You can use namespaces that contain identically named classes or methods, but you will only be notified of a conflict if you try to use a class or method that is duplicated in more than one namespace.

The most common namespace is the System namespace, and it is imported by default without your needing to declare it. It contains many of the most fundamental classes and methods that C# uses for access to basic classes such as Application, Array, Console, Exceptions, Objects, and standard objects such as byte, bool, string. In the simplest C# program we can simply write a message out to the console without ever bringing up a window or form:

class Hello {

static void Main(string[] args) {

Console.WriteLine ("Hello C# World");

}

}

This program just writes the text “Hello C# World” to a command (DOS) window. The entry point of any program must be a Main method, and it must be declared as static.