by Administrator
18. May 2009 14:16
In C#, you use the class keyword to define a new class. The data and methods of the class oc-
cur in the body of the class between a pair of braces. Here is a C# class called Circle that con-
tains one method (to calculate the circle’s area) and one piece of data (the circle’s radius):
class Circle
{
double Area()
{
return Math.PI * radius * radius;
}
int radius;
}
The body of a class contains ordinary methods (such as Area) and fields (such as radius)—
remember that variables in a class are called fields. You’ve already seen how to declare vari-
ables in Chapter 2, “Working with Variables, Operators, and Expressions,” and how to write
methods in Chapter 3, “Writing Methods and Applying Scope”; in fact, there’s almost no new
syntax here.
Using the Circle class is similar to using other types that you have already met; you create a
variable specifying Circle as its type, and then you initialize the variable with some valid data.
Here is an example:
Circle c; // Create a Circle variable
c = new Circle(); // Initialize it
Note the use of the new keyword. Previously, when you initialized a variable such as an int or
a float, you simply assigned it a value:
int i;
i = 42;
You cannot do the same with variables of class types. One reason is that C# just doesn’t pro-
vide the syntax for assigning literal class values to variables
Another reason concerns the way in which memory for variables of class types is al-
located and managed by the runtime
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Tags: c#