abstract class Parent { int i = 9;
void display() {
System.out.println("base");
}
}
class Child extends Parent { int i = 8;
public void display() {
System.out.println("derived");
}
}
public class A {
public static void main(String args[]) {
Parent a1 = new Child();
a1.display(); // calls child class method
System.out.println(a1.i);// calls parent class member
}
}
You cannot access Parent class display() method directly without creating an object of it.
But you can access it from you child class.like this
class Child extends Parent {
int i = 8;
public void display() {
super.display();
System.out.println("derived");
}
}
According to java docs Accessing Superclass Members
If your method overrides one of its superclass's methods, you can invoke the overridden method through the use of the keyword super. You can also use super to refer to a hidden field (although hiding fields is discouraged).
when i run this code display method of derived class is being called
Looks like you have programmed in other programming languages like C++ or C# where you must specify the method as virtual in order to use the subclass method. In Java, all the methods except private, final and static are virtual.
Knowing this, since Child class already overrides display method from Parent class, when you do this:
Parent a1 = new Child();
a1.display();
a1.display will execute the display method of the actual object reference class, in this case, Child#display.
In order to fix the code, change the initialization of a1 to be a new Parent:
Parent a1 = new Parent();
a1.display();
More info:
After your edit, now you face the problem when printing a1 in the console, probably printing 9 instead of 8. What you're doing here is hiding the field. Fields do not get overridden, so the value of the i variable will depend on the actual class type declared for the variable. Since you have declared a1 as Parent, then a1.i will take the value of Parent#i.
In order to fix this code, change the a1 variable type to Child:
Child a1 = new Child();
System.out.println(a1.i);
a1.display();
Or a even better solution: NEVER try to override a field, and what's worse, don't try to access to class fields from other classes directly, instead use the respective getters and setters.
More info:
How to access methods of ancestor class when intermediate parent class overrides it?
Assuming this is your real question, then the answer is simple: you can't.
If I understand your question right you are trying to invoke the PARENTS display method using CHILD instance.
With just the derived class object there's NO way to instruct the compiler to make the non-virtual call to the base-class version.
You just cannot. If you want the code in parent class to be executed then you either have to create a parent class (note: Parent is not abstract class) or you have to provide call to super.someMethod() in one of the methods of the child. For example:
public void display() {
super.display();
System.out.println("derived");
}
I think what you are trying to ask is why the variables of parent class is displayed and method of child class.
Firstly, overriding is not applied to variables,it is applied on methods. Whatever class the reference belongs to, that variable will be displayed straight away.In your code,
Parent a1 = new Child();
System.out.println(a1.i);
Here a1 is a reference to Parent class, so variable of Parent class is displayed.
In case of methods, it is decided at run time which version of methods would be called. That method is called whose object is created, here object of Child class is crated Parent a1 =new Child(); . See the part new Child() and hence the Child class method. But remember, this method should be present in the class that the reference belongs. For example
Class Parent
{
}
Class Child extends Parent
{
public void display()
{
System.out.println("derived");
}
public static void main (String []args)
{
Parent a1 = new Child();
a1.display(); //Error
}
}
To call the base class method in your original example, use super as others have mentioned. Or simply create an object of parent class
Parent o = new Parent();
o.display(); //prints base
