Notes

import java.util.*;

class AreaTriangle{
double a,b,c;
double area()
{
double s=(a+b+c)/2.0;
double area=Math.sqrt(s*(s-a)*(s-b*(s-c)));
return area;
}
}
class AreaSquare extends AreaTriangle{
double area()
{
return a*a;
}
}
class AreaRectangle extends AreaSquare{
double area()
{
return a*b;
}
}
class AreaCircle extends AreaRectangle{
double area()
{
return Math.PI*a*a;
}
}
class AreaCalculate
{
public static void main(String args[])
{
int opt;
AreaTriangle at=new AreaTriangle();
AreaSquare as=new AreaSquare();
AreaRectangle ar=new AreaRectangle();
AreaCircle ac=new AreaCircle();
System.out.println("Which area you want to calculate?n1.Trianglen2.Squaren3.Rectanglen4.CirclennEnter your choice :");
Scanner sc=new Scanner(System.in);
opt=sc.nextInt();
if(opt==1)
{
System.out.println("Enter 3 sides of triangle :");
at.a=sc.nextDouble();
at.b=sc.nextDouble();
at.c=sc.nextDouble();
System.out.println("Area of Triangle : "+at.area());
}
else if(opt==2)
{
at=as;
System.out.println("Enter side of square :");
at.a=sc.nextDouble();
System.out.println("Area of Triangle : "+at.area());
}
else if(opt==3)
{
at=ar;
System.out.println("Enter sides of rectangle :");
at.a=sc.nextDouble();
at.b=sc.nextDouble();
System.out.println("Area of Rectangle : "+at.area());
}
else if(opt==4)
{
at=ac;
System.out.println("Enter radius of Circle :");
at.a=sc.nextDouble();
System.out.println("Area of Circle : "+at.area());
}
}
}