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C# Classes and Objects


Classes and Objects

You learned from the previous chapter that C# is an object-oriented programming language.

Everything in C# is associated with classes and objects, along with its attributes and methods. For example: in real life, a car is an object. The car has attributes, such as weight and color, and methods, such as drive and brake.

A Class is like an object constructor, or a "blueprint" for creating objects.


Create a Class

To create a class, use the class keyword:

Create a class named "Car" with a variable color:

class Car 
{
  string color = "red";
}

When a variable is declared directly in a class, it is often referred to as a field (or attribute).

It is not required, but it is a good practice to start with an uppercase first letter when naming classes. Also, it is common that the name of the C# file and the class matches, as it makes our code organized. However it is not required (like in Java).


Create an Object

An object is created from a class. We have already created the class named Car, so now we can use this to create objects.

To create an object of Car, specify the class name, followed by the object name, and use the keyword new:

Example

Create an object called "myObj" and use it to print the value of color:

class Car 
{
  string color = "red";

  static void Main(string[] args)
  {
    Car myObj = new Car();
    Console.WriteLine(myObj.color);
  }
}

Run example »

Note that we use the dot syntax (.) to access variables/fields inside a class (myObj.color). You will learn more about fields in the next chapter.


Multiple Objects

You can create multiple objects of one class:

Example

Create two objects of Car:

class Car
{
  string color = "red";

  static void Main(string[] args)
  {
    Car myObj1 = new Car();
    Car myObj2 = new Car();
    Console.WriteLine(myObj1.color);
    Console.WriteLine(myObj2.color);
  }
}

Run example »


Using Multiple Classes

You can also create an object of a class and access it in another class. This is often used for better organization of classes (one class has all the fields and methods, while the other class holds the Main() method (code to be executed)).

  • Car.cs
  • Program.cs

Car.cs

class Car {
  public string color = "red";
}

Program.cs

class Program
{
  static void Main(string[] args)
  {
    Car myObj = new Car();
    Console.WriteLine(myObj.color);
  }
}

Run example »

Did you notice the public keyword? It is called an access modifier, which specifies that the color variable/field of Car is accessible for other classes as well, such as Program.

You will learn much more about access modifiers and classes/objects in the next chapters.