1. By means of
sub class object it is possible to access all the instance variables and
instance methods of the super class.
2.
By means of sub class object it cannot be possible to access the instance
variable of super class, if it is declared as private. Since, the data is protected in that class.
import
javax.swing.JOptionPane;
class
student
{
private int rno;
void readdata1()
{
rno=Integer.parseInt(JOptionPane.showInputDialog("Enter
roll number"));
}
}
class
exam extends student
{
void printdata1()
{
readdata1();
System.out.println("Roll
Number="+rno); // produces
compilation error
}
}
class
mi2
{
public static void main(String[]
args)
{
exam
obj=new exam();
obj.printdata1();
}
}
3.
Referring to super class object with a subclass reference produces syntax
error. In such case we need type
casting.
Example:
import
javax.swing.JOptionPane;
class
student
{
int rno;
void readdata1()
{
rno=Integer.parseInt(JOptionPane.showInputDialog("Enter
roll number"));
}
}
class
exam extends student
{
void printdata1()
{
readdata1();
System.out.println("Roll
Number="+rno);
}
}
class
mi2
{
public static void main(String[]
args)
{
student s1=new exam();
exam e1=(exam)s1;
e1.printdata1();
}
}
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