Page 450 - Computer science 868 Class 12
P. 450
• The super() keyword is also used to invoke a parent class constructor. Default super class constructor is implicitly
called by its derived class constructor. For parameterised base class constructor, the constructor invocation should
be the first statement in derived class constructor definition.
To demonstrate the usage of the keyword super, let us write small programs by taking three classes given below.
Base class Circle
Data member
double r to store radius
Circle(double rr) Assign r = rr
void display() Displays radius
Derived class Area
Data member
double a to store area
double findarea() Calculates and returns area of a
circle as πr 2
void display() Displays radius and area
Derived class Circumference
Data member
double c to store circumference
double findcircumference() Calculates and returns circumference
of a circle as 2πr
void display() Displays radius and circumference
class Circle
{ protected double r; // visibility mode
Circle(double rr)
{ r=rr;}
void display()
{ System.out.println("Radius="+r);} }
class Area extends Circle // defining derived class
{ double a;
Area(double ra)
{ super(ra); // invoking super class constructor
a=0.0; }
double findarea()
{ /* Member data r belongs to base class can be accessed
by derived class due to inheritance */
return Math.PI*r*r; }
void display()
{ a=findarea();
super.display(); // method overriding
System.out.println("Area ="+a);
} }
class Circumference extends Circle // defining derived class
{ double c;
Circumference(double ra)
{ super(ra); // invoking super class constructor
c=0.0; }
448448 Touchpad Computer Science-XII

