Why the o/p is not what it is expected ?

[faisal usmani]

Why output is (10 dervied) and not (20 derived)???


class Par
{
public static void main(String args[])
{
A z = new B();
System.out.println(z.a);
z.display();
}
}


class A
{
int a=10;


void display()
{
System.out.println("base");
}
}

class B extends A
{
int a=20;


void display()
{
System.out.println("derived");
}
}

output::
10
derived

[Ernest Friedman-Hill]

Because variables aren't polymorphic the way methods are. You can't "override a variable". In main, you've got a reference to class A, and you ask for the "a" variable, so you get the "a" variable of class A. There's no special relationship between the two "a" variables as there is between the two "display" methods.