Creating a Simple Class in C# (2)

Instantiating the Class

Although we have not explicitly added any functionality to the class, it can now be instantiated to create objects. These objects will have the standard behaviour of all classes. To demonstrated this, return to the program code file containing the Main method. In this method we will create a new vehicle object and run its ToString method to see the results. As we have not yet defined how ToString should work, this will simply show the fully qualified name.

static void Main(string[] args)
{
    Vehicle car = new Vehicle();
    Console.WriteLine(car.ToString());  // Outputs "ClassTest.Vehicle"
}

NB: The prefix of ClassTest is simply the name of the namespace of the Vehicle class.

Adding Methods

Public Methods

Public methods are part of the class' public interface, ie. these are the methods that can be called by other objects.

• C# Methods
• C# Functional Methods
• C# Method Parameters

The syntax for creating methods described in the above articles must be modified slightly to make the methods visible to external objects. To achieve this, the public keyword is used as a prefix. The following code added to the vehicle class provides a new method for pressing a vehicle's horn. Make sure that you add the code within the class' code block.

public void PressHorn()
{
    Console.WriteLine("Toot toot!");
}

To use the new method, change the code within the Main method as follows:

static void Main(string[] args)
{
    Vehicle car = new Vehicle();
    car.PressHorn();                    // Outputs "Toot toot!"
}

Private Methods

To provide for encapsulation, where the internal functionality of the class is hidden, some methods will be defined as private. Methods with a private protection level are completely invisible to external classes. This makes it safe for the code to be modified to change functionality, improve performance, etc. without the need to update classes that use the public interface. To define a method as private, the private keyword can be used as a prefix to the method. Alternatively, using no prefix at all implies that the method is private by default.
The following method of the car class is a part of the internal implementation not the public interface so is defined as being private.

private void MonitorOilTemperature()
{
    // Internal oil temperature monitoring code...;
}

To demonstrate that this method is unavailable to external classes, try the following code in the Main method of the program. When you attempt to compile or execute the program, an error occurs indicating that the MonitorOilTemperature method cannot be called due to its protection level.

static void Main(string[] args)
{
    Vehicle car = new Vehicle();
    car.MonitorOilTemperature();
}

Limitations

This article has described the creation of a basic class with public and private methods. However, every object that is generated from this class is identical, as it currently has no state. In the next article in the series, we will add properties to the class to resolve this.