AP Computer Science Exam Question

1. Create a class called "Circle" with the following attributes and methods:

   • Attributes:
     • radius (a floating-point number)
   • Methods:
     • calculate_area() - returns the area of the circle (π * radius * radius)

2. Create an object of the "Circle" class with a radius of 5.0 and compute the area of the circle.

Answer

public class Circle {
    private double radius;

    public Circle(double radius) {
        this.radius = radius;
    }

    public double calculateArea() {
        return Math.PI * radius * radius;
    }

    public static void main(String[] args) {
        Circle myCircle = new Circle(5.0);
        double area = myCircle.calculateArea();
        System.out.println("The area of the circle is: " + area);
    }
}

Explanation:

• The Circle class is created with a private attribute radius and a constructor to initialize the radius.
• The calculateArea method computes the area of the circle using the formula π * radius * radius.
• In the main method, an object myCircle of the class Circle is created with a radius of 5.0.
• The calculateArea method is then called on myCircle to compute the area of the circle, which is then printed to the console.