What is the difference between an abstract functio

Question

What is the difference between an abstract function and a virtual function? In which cases is it recommended to use virtual or abstract? Which one is the best approach?

Answer 1

I have seen in some places the abstract method is defined as below. **

"An Abstract Method must have to implement in the child class"

** I felt it is like .

It is not necessary that an abstract method has to be implemented in a child class, if the child class is also abstract ..

1)An abstract method cant be a private method. 2)An Abstract method cant be implemented in the same abstract class.

I would say ..if we are implementing an abstract class, you must have to override the abstract methods from the base abstract class. Because.. Implementing the abstract method is with override key word .Similar to Virtual method.

It is not necessary for a virtual method to be implemented in an inherited class.

                                 ----------CODE--------------

public abstract class BaseClass
{
    public int MyProperty { get; set; }
    protected abstract void MyAbstractMethod();

    public virtual void MyVirtualMethod()
    {
        var x = 3 + 4;
    }

}
public abstract class myClassA : BaseClass
{
    public int MyProperty { get; set; }
    //not necessary to implement an abstract method if the child class is also abstract.

    protected override void MyAbstractMethod()
    {
        throw new NotImplementedException();
    }
}
public class myClassB : BaseClass
{
    public int MyProperty { get; set; }
    //You must have to implement the abstract method since this class is not an abstract class.

    protected override void MyAbstractMethod()
    {
        throw new NotImplementedException();
    }
}

Answer 2

To my understanding:

Abstract Methods:

Only the abstract class can hold abstract methods. Also the derived class need to implement the method and no implementation is provided in the class.

Virtual Methods:

A class can declare these and also provide the implementation of the same. Also the derived class need to implement of the method to override it.

Answer 3

1. Only abstract classes can have abstract members.
2. A non-abstract class that inherits from an abstract class must override its abstract members.
3. An abstract member is implicitly virtual.
4. An abstract member cannot provide any implementation (abstract is called pure virtual in some languages).

Answer 4

explanation: with analogies. hopefully it will help you.

Context

I work on the 21 st floor of a building. And I'm paranoid about fire. Every now and again, somewhere in the world, a fire is burning down a sky scraper. But luckily we have an instruction manual somewhere here on what to do in case of fire:

FireEscape()

1. Don't collect belongings
2. Walk to fire escape
3. Walk out of building

This is basically a virtual method called FireEscape()

Virtual Method

This plan is pretty good for 99% of the circumstances. It's a basic plan which works. But there is a 1% chance that the fire escape is blocked or damaged in which case you are completely screwed and you'll become toast unless you take some drastic action. With virtual methods you can do just that: you can override the basic FireEscape() plan with your own version of the plan:

1. Run to window
2. Jump out the window
3. Parachute safely to the bottom

In other words virtual methods provide a basic plan, which can be overriden if you need to. Subclasses can override the parent class' virtual method if the programmer deems it appropriate.

Abstract methods

Not all organisations are well drilled. Some organisations don't do fire drills. They don't have an overall escape policy. Every man is for himself. Management are only interested in such a policy existing.

In other words, each person is forced to develop his own FireEscape() method. One guy will walk out the fire escape. Another guy will parachute. Another guy will use rocket propulsion technology to fly away from the building. Another guy will abseil out. Management don't care how you escape, so long as you have a basic FireEscape() plan - if they don't you can be guaranteed OHS will come down on the organisation like a tonne of bricks. This is what is meant by an abstract method.

What's the difference between the two again?

Abstract method: sub classes are forced to implement their own FireEscape method. With a virtual method, you have a basic plan waiting for you, but can choose to implement your own if it's not good enough.

Now that wasn't so hard was it?

Answer 5

Abstract function(method) :

● An abstract method is a method which is declared with the keyword abstract.

● It does not have body.

● It should be implemented by the derived class.

● If a method is abstract then the class should abstract.

virtual function(method) :

● A virtual method is the method which is declared with the keyword virtual and it can be overridden by the derived class method by using override keyword.

● It's up to the derived class whether to override it or not.

Answer 6

Abstract function cannot have a body and MUST be overridden by child classes

Virtual Function will have a body and may or may not be overridden by child classes