Inheritance Test in Java

//[1]What is the Error?

class A{
public  int i;

public  void seti(int ii){
i =ii;
}

public void printi(){
System.out.println("i =  "+i);
}
}

class B extends A{
public void modi(){
i = i+8;
}
}

class TestC8{
public static void main(String...arg){
A ob1 =  new A();
B ob2 = (B)ob1; //we try to cast super class to sub class

}
}




//Note:
// Rule  : cast super class ref var  to sub class
//         it is Ok at compile time but failes at runtime!!

--------------------------------------------


//[2]What is the output?



class A{
public  int i;

public  void seti(int ii){
i =ii;
}

public void printi(){
System.out.println("i =  "+i);
}
}

class B extends A{
public void modi(){
i = i+8;
}
}

class TestC7{
public static void main(String...arg){
A ob1;
B ob2 = new B();
ob1 = ob2; //super class is reffering subclass object
ob1.seti(6);
ob1.printi();
B ob3= (B)ob1; //casting super class var to sub class
ob3.modi();
ob3.printi();



}
}