1 public class Circle { 2 3 // Class variable: 4 protected final static double PI = 3.14159265358979323846; 5 6 // Instance variable: 7 protected double r; // the radius of the circle 8 9 // Constructors: 10 public Circle(double r) { 11 setRadius(r); 12 } 13 public Circle() { } 14 15 // Encapsulate the radius: 16 public void setRadius(double r) { 17 this.r = r; 18 } 19 public double getRadius() { 20 return r; 21 } 22 23 // Instance methods: 24 public double circumference() { 25 return 2*PI*r; 26 } 27 public double area() { 28 return PI*r*r; 29 } 30 }