Why can't an object of abstract class be created?

Question

Here is a scenario in my mind and I have googled, Binged it a lot but got the answer like

\"Abstract class has not implemented method so, we cant create the object\

Answer 1

The reference studytonight :

When we create a pure virtual function in Abstract class, we reserve a slot for a function in the VTABLE(studied in last topic), but doesn't put any address in that slot. Hence the VTABLE will be incomplete.

As the VTABLE for Abstract class is incomplete, hence the compiler will not let the creation of object for such class and will display an errror message whenever you try to do so.

Answer 2

As an addition to the other answers, you may not be able to create an instance of the abstract class, but you can certainly refer to instances of derived types through the abstract type and use methods or properties that are defined within the abstract base.

abstract class A
{
    public abstract void D();
    public void E() { }
}

class B : A
{
    public override void D() { }
}

class C : A
{
    public override void D() { }
}

...

A a = new B();
a.D();
a.E();

List<A> list = new List<A>() { new B(), new C() };

Answer 3

Sorry guys...

You can Create object for an abstract class, if and only if that abstract class does not contains any abstract method.

Here is my Example. Copy it and compile and run.

abstract class Example {
  void display(){
    System.out.println("Hi I am Abstract Class.");
  }
}

class ExampleDemo {
    public static void main(String[] args) {
        Example ob = new Example(){};
        ob.display();
   }
}

So your answer is yes, we can create object for abstract class if it's no Abstract Method. Check my program.

Answer 4

We cannot create object for abstract class bcoz ,mostly abstract class contain "abstract methods" ,so abstract methods are incomplete methods.so we cannot estimate the memory of those methods how much they are going to occupy .This is one of the reason why we cannot create object for abstract class.

Answer 5

I don't agree with the accepted answer. The reason is that we can have body for pure virtual function.

The answer is that :

When we create a pure virtual function in the class, we reserve a slot for a function in the VTABLE, but doesn't put any address in that slot. Hence the VTABLE will be incomplete. As the VTABLE for Abstract class is incomplete, hence the compiler will not let the creation of object for such class and will display an error message whenever you try to do so.

Answer 6

Because it's abstract and an object is concrete. An abstract class is sort of like a template, or an empty/partially empty structure, you have to extend it and build on it before you can use it.

Take for example an "Animal" abstract class. There's no such thing as a "pure" animal - there are specific types of animals. So you can instantiate Dog and Cat and Turtle, but you shouldn't be able to instantiate plain Animal - that's just a basic template. And there's certain functionality that all animals share, such as "makeSound()", but that can't be defined on the base Animal level. So if you could create an Animal object and you would call makeSound(), how would the object know which sound to make?