Introduction to OOP in C#: Classes - Page 1
       by kirupa  |  5 January 2007

In the previous page you created a class and learned about constructors. We will pick up from where we left off and learn how to add more functionality to our class using methods.

Methods (Functions)
Right now, our Planet class only contains fields and a constructor. Constructors are great for simply creating your object and initializing fields, but beyond that, they cannot help you. In order to have your class do more interesting things, you will need to use what are called methods.

In a nutshell, a method is a block of code that does something specific. It has a name and various tags (properties) that describe its behavior. More importantly, methods also have the ability to return data back to whoever called it. For example, you probably have been using a method called Main to test your programs:

static void Main(string[] args)

{

Planet earth = new Planet(6378, 9.81, "Earth");

 

Console.WriteLine("Earth's radius is: " + earth.radius);

}

To best describe the individual parts that make up a method, let's look at the following image:

Your method declaration follows the template shown in the above image. The following list explains what each part means:

• Access Modifier
  Access modifiers define how easily accessible your method will be, and this will be very important when I explain inheritance. The access modifiers we learned so far are public and private, and the other modifiers, which I will cover on a later date, are protected, static, internal, readonly, volatile, new, and protected internal.
• Return Type
  The type of an object is basically the class it belongs to. The return-type is then the type of the data you are returning when the method is called. If you set your return type to void, that means that you are not sending any data back. We'll see an example of this in use shortly.
• Method Name
  This is pretty easy! This is just the name you give your method.
• Arguments (arg1, arg2,..., arg N)
  Your method can take in values much like how our constructor took in values to assign values to our fields.
• Body of Method
  Your method's code would go here.

Now that you have a basic idea of what goes into a method, let's look at the first type of method I will cover, Instance Methods.

Instance Methods
Instance methods are methods you call from a object. The best way to explain it is via an example. For the past few pages, we have tried to get data from our name field to display when accessed via our object. Let's use a method to do that right now.

Add the following non-grayed out code to your Planet class:

class Planet

{

public int radius;

public double gravity;

private string name;

 

// A Constructor

public Planet(int r, double g, string n)

{

radius = r;

gravity = g;

name = n;

}

 

//Return the object's name!

public string GetName()

{

return name;

}

}

More specifically, the code you added is shown below:

//Return the object's name!

public string GetName()

{

return name;

}

Let's dissect our GetName() method. Notice that its return type is string, and in the body of our method, we return the name field which is also of type string. The return type of your method must match the return type of the value being returned. Finally, notice that the access modifier of our method is public. Guess what that means?

You'll find out when you add the following code to your Main method:

static void Main(string[] args)

{

Planet earth = new Planet(6378, 9.81, "Earth");

 

Console.WriteLine("Earth's radius is: " + earth.radius);

Console.WriteLine("Earth's name is: " + earth.GetName());

}

Notice that when you run your application by pressing Ctrl + F5, you will see not only the radius being being displayed, but the name is also displayed:

[ your output window with the radius and name information displayed ]

The reason the name is displayed is because while the name field is private, the method that returns the value is public. Our goal was to hide the name field, but not to hide the GetName() method. Since GetName() is within our Planet class definition, returning the private name field is allowed.

Onwards to the next page!

1 | 2 | 3 | 4