public class Circle {

private double radius;

public Circle() {

radius = 1;

}

public Circle(double r) {

radius = r;

}

public double diameter() {

return radius*2;

}

public double circumference() {

return 2*Math.PI*radius;

}

public double area() {

return Math.PI*radius*radius;

}

public static void main(String[] args) {

Circle c = new Circle();

System.out.println("The diameter of circle c is " + c.diameter());

System.out.println("The circumference of circle c is " + c.circumference());

System.out.println("The area of circle c is " + c.area());

Circle c1 = new Circle(7);

System.out.println("The diameter of circle c1 is " + c1.diameter());

System.out.println("The circumference of circle c1 is " + c1.circumference());

System.out.println("The area of circle c1 is " + c1.area());

}

//todo: add some methods to compute a circle's diameter, circumference and area.

//print some outputs to confirm you methods are working right.

}