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  }