Practical Coding in Java

//
// Circle.java
//


public class Circle
{
    public Circle(double radiusIn)
    {
        radius = radiusIn;
    }

    public double circumference()
    {
        return 2 * Math.PI * radius;
    }

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

    // we can override the default toString() function,
    // which println() calls when printing an object

    public String toString()
    {
        return "Circle (radius=" + radius + ")";
    }

    private double radius;
}

//
// CircleTest.java
//


public class CircleTest
{
    public static void main(String[] args)
    {
        Circle c = new Circle(1);
        System.out.println(c);
        System.out.println("circumference: " + c.circumference());
        System.out.println("area: " + c.area());
        System.out.println();

        Circle d = new Circle(10);
        System.out.println(d);
        System.out.println("circumference: " + d.circumference());
        System.out.println("area: " + d.area());
    }
}