C# 4 and .NET 4

implementation inheritance ❘ 91
If you do not specify a base class in a class definition, the C# compiler will assume that System.Object is
the base class. Hence, the following two pieces of code yield the same result:
and
class MyClass: Object // derives from System.Object
{
// etc.
}
class MyClass // derives from System.Object
{
// etc.
}
For the sake of simplicity, the second form is more common.
Because C# supports the object keyword, which serves as a pseudonym for the System.Object class, you
can also write:
class MyClass: object // derives from System.Object
{
// etc.
}
If you want to reference the Object class, use the object keyword, which is recognized by intelligent
editors such as Visual Studio .NET and thus facilitates editing your code.
Virtual methods
By declaring a base class function as virtual, you allow the function to be overridden in any
derived classes:
class MyBaseClass
{
public virtual string VirtualMethod()
{
return "This method is virtual and defined in MyBaseClass";
}
}
It is also permitted to declare a property as virtual. For a virtual or overridden property, the syntax is
the same as for a nonvirtual property, with the exception of the keyword virtual, which is added to the
definition. The syntax looks like this:
public virtual string ForeName
{
get { return foreName;}
set { foreName = value;}
}
private string foreName;
For simplicity, the following discussion focuses mainly on methods, but it applies equally well to properties.
The concepts behind virtual functions in C# are identical to standard OOP concepts. You can override a
virtual function in a derived class, and when the method is called, the appropriate method for the type of
object is invoked. In C#, functions are not virtual by default but (aside from constructors) can be explicitly
declared as virtual. This follows the C++ methodology: For performance reasons, functions are not virtual
unless indicated. In Java, by contrast, all functions are virtual. C# does differ from C++ syntax, though,
because it requires you to declare when a derived class’s function overrides another function, using the
override keyword:
class MyDerivedClass: MyBaseClass
{
public override string VirtualMethod()
www.it-ebooks.info