Doubt on basic concept

Question

Say we have a class called Animal which has a method called shout().
we have another class called Dog which has a method callled bark().
Dog class extends Animal class.
so Dog class has 2 methods now
1)shout()
2)bark()
If we declare like this
Animal a=new Animal();//valid statement
a.shout();//valid statement
Dog d=new Dog();//valid statement
d.shout();//valid statement
d.bark();//valid statement
Animal a=new Dog();
a.shout();//valid statement
a.bark();//invalid since type of reference variable is Animal
Dog d=new Animal();
why the above decalration is not valid?
Animal object has shout() method
By inheritance Dog class has both shout() and bark() methods.
So with above type of declaration d.shout() should execute.But that is wrong.
A subclass reference variable cannt point to a subclass object.I know this kind of statement.But can any one explain why?

Answer 1

kirn291 wrote:
Dog d=new Animal();
why the above decalration is not valid?To a Dog variable you can only assign objects which are of type Dog, and Animal isn't.
A Dog object is both of type Dog and of type Animal. This means Dog objects can be assigned to both Dog variables and Animal variables.