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);
}
}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);
}
}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);
}
}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.
