// Beispiel: ..\Kapitel 3\GeometricObjectsSolution_1
public class Circle {
  // ---------- Klasseneigenschaft -----------------
  private static int _CountCircles;
  public static int CountCircles {
    get { return _CountCircles; }
  }
  // --------- Konstruktoren ---------------
  public Circle() : this(0, 0, 0) { }
  public Circle(int radius) : this(radius, 0, 0) { }
  public Circle(int radius, double x, double y) {    
    Radius = radius;
    XCoordinate = x;
    YCoordinate = y;
    Circle._CountCircles++;
  }
  // -------- Eigenschaften ----------
  public double XCoordinate { get; set; }
  public double YCoordinate { get; set; }
  private int _Radius;
  public int Radius {
    get { return _Radius; }
    set {
      if (value >= 0)
        _Radius = value;
      else
        Console.WriteLine("Unzulässiger negativer Radius.");
    }
  }
  // ---------- Instanzmethoden ----------
  public double GetArea() {
    return Math.Pow(Radius, 2) * Math.PI;
  }
  public double GetCircumference() {
    return 2 * Radius * Math.PI;
  }
  public int Bigger(Circle kreis) {
  if (kreis == null || Radius > kreis.Radius) return 1;
  if (Radius < kreis.Radius) return -1;
  else return 0;
  }
  public void Move(double dx, double dy) {
    XCoordinate += dx;
    YCoordinate += dy;
  }
  public void Move(double dx, double dy, int dRadius) {
    XCoordinate += dx;
    YCoordinate += dy;
    Radius += dRadius;
  }
  // -------- Klassenmethoden ------------
  public static double GetArea(int radius) {
    return Math.Pow(radius, 2) * Math.PI;
  }   
  public static double GetCircumference(int radius) {
    return 2 * radius * Math.PI;
  }
  public static int Bigger(Circle kreis1, Circle kreis2) {
    if (kreis1 == null && kreis2 == null) return 0;
    if (kreis1 == null) return -1;
    if (kreis2 == null) return 1;
    if (kreis1.Radius > kreis2.Radius) return 1;
    if (kreis1.Radius < kreis2.Radius) return -1;
    return 0;
  }
}