当对象被超类引用时，有没有办法访问子对象的变量？

Question

Is there any other way to access child object's variable when the object is referred by its parent class other than casting the object to child class?

class parent{
   int parentData;
}

class child extends parent{
   int childData;
}

parent obj =new child();
obj.childData =10 ;            //is getting error
((child )obj).childData=10;    // is working fine

is there any other way to access child class variable where child class object is pointed by parent class ?

scenario

If my parent class has 2-3 child class that are differ with parent class by only one variable and i tried to refer all child class object with parent class.In some point i need to get child variable what should i do ? do i need to redesign ?

Answer 1

The parent class should contain only behavior that is common to all child classes.

If what you are trying to implement in the parent class is indeed common behavior you might want to look in to the Template method pattern .

If what you are implementing is different behavior over the child classes, do not try to shoehorn it into the parent class but implement it in the child classes. If these implementations share common parts, you could extract this to a common method either in the parent or a helper class.

Answer 2

How come parents started to know thier childs in java? That's not possible.