Here is some code from MSDN:
// compile with: /target:library
public class D
{
public virtual void DoWork(int i)
{
// Original implementation.
}
}
public abstract class E : D
{
public abstract override void DoWork(int i);
}
public class F : E
{
public override void DoWork(int i)
{
// New implementation.
}
}
Can anyone explain the above code with respect to the differences between abstract and virtual methods?
Virtual methods have an implementation and provide the derived classes with the option of overriding it. Abstract methods do not provide an implementation and force the derived classes to override the method.
So, abstract methods have no actual code in them, and (non-abstract) subclasses HAVE TO override the method. Virtual methods can have code, which is usually a default implementation of something, and any subclasses CAN override the method using the override modifier and provide a custom implementation.
public abstract class E
{
public abstract void AbstractMethod(int i);
public virtual void VirtualMethod(int i)
{
// Default implementation which can be overridden by subclasses.
}
}
public class D : E
{
public override void AbstractMethod(int i)
{
// You HAVE to override this method
}
public override void VirtualMethod(int i)
{
// You are allowed to override this method.
}
}
override for the abstract method in the child class [because it is required it be overwritten]? –
Mond override keyword there, the original method will become hidden. If this is your intention, you can use new keyword to get rid of the warning, but cases where you want to hide methods are pretty rare. So unless you specifically want to use method hiding, you should always use the override keyword –
Stephenstephenie First of all you should know the difference between a virtual and abstract method.
Abstract Method:
If an abstract method is defined in a class, then the class should declare as an abstract class.
An abstract method should contain only method definition, should not Contain the method body/implementation.
An abstract method must be over ride in the derived class.
Virtual Method:
Example:
public abstract class baseclass
{
public abstract decimal getarea(decimal Radius);
public virtual decimal interestpermonth(decimal amount)
{
return amount*12/100;
}
public virtual decimal totalamount(decimal Amount,decimal principleAmount)
{
return Amount + principleAmount;
}
}
public class derivedclass:baseclass
{
public override decimal getarea(decimal Radius)
{
return 2 * (22 / 7) * Radius;
}
public override decimal interestpermonth(decimal amount)
{
return amount * 14 / 100;
}
}
an abstract method must be call override in derived class other wise it will give compile-time error and in virtual you may or may not override it's depend if it's good enough use it
Example:
abstract class twodshape
{
public abstract void area(); // no body in base class
}
class twodshape2 : twodshape
{
public virtual double area()
{
Console.WriteLine("AREA() may be or may not be override");
}
}
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DoWork()method is optional for all it's immediate-children/subclasses. The code above adds an intermediary abstract Class-E to force the overriding of Class-D'sDoWork()method for all subclasses of Class-E - essentially preventing all of Class-E's children from using Grandpa-Class-D'sDoWork(). In other words: the implementation of Class-D'sDoWork()is hidden from Class-F; and it is now compulsory for Class-F (and all it's sibling classes) to each form their own custom implementation ofDoWork(). – Sliest