About
abstract class, interfaces, virtual & hiding with new in c sharp
Abstract
class:
An abstract class is
a special type of class that cannot be instantiate. The abstract class is only
to be inherited and we can create object for subclasses. In abstract class we
can define abstract methods. Abstract members are like virtual members but they
don’t provide default implementation. The implementation will be provided by
subclass.
Virtual members:
A function marked as
the virtual can be overridden by
subclasses wanting to provide a specialized implementation. Not only the
methods but also the properties, indexers and events can be declared as can be
declared as virtual.
New keyword:
A base class and
derived class may have identical members. Then the member in the derived class
said to hide the member in the base class.
Example:
public class
BaseClass
{
public int counter=1;
}
public class DerivedClass:
Baseclass
{
public int counter=5;
}
The counter field in
Derived class is said to hide the counter field in the Baseclass. but when
compiling a warning will be generated. The warning will be suppressed if we
declare subclass member with the new keyword.
Example:
public class
BaseClass
{
public int counter=1;
}
public class DerivedClass:
Baseclass
{
public new int
counter=5;
}
Difference between overriding and hiding with
new keyword.
public class
BaseClass
{
public virtual void
Test()
{
Console.WriteLine(“BaseClass::test”);
}
}
public class DerivedClass:
BaseClass
{
{
public new void Test()
{
Console.writeLine(“DerivedClass::Test”);
}
}
public class overrided:
BaseClass
{
public override void
Test()
{
Console.WriteLine(“Overrided::Test()”);
}
}
}
Differences for above classes:
Overrided o=new
overrieded();
Baseclass b=o;
o.Test() ;
//overrided::test()
b.Test(); // overrided::test()
DerivedClass d=new
DerivedClass()
BaseClass b=d;
d.Test() ; //DerivedClass::Test()
b.Test();
//Baseclass::Test()
from the above example it is clear that incase
of overriding when assigning derived class object to base class object calling
to method calls the overrided method. But in case of hiding derived class
object when assigning derived class object to base class object calling to
method only calls the base class method.
Interfaces
An interface is not a
class. It is an entity that is defined by the word Interface. Interfaces provides the
specification rather than an implementation for its members. A class can
implement multiple interfaces while a class can inherit only a single class. Interface
members are implicitly abstract while a class can provide only abstract members
and concrete members with implementations. Struts can implement a class but a
struct cannot inherit from a class.
