public class CenteredRectangle extends Rectangle implements Centered {
  // New instance fields
  private double cx, cy;

  // A constructor
  public CenteredRectangle(double cx, double cy, double w, double h) { 
    super(w, h); 
    this.cx = cx;
    this.cy = cy;
  }

  // We inherit all the methods of Rectangle but must
  // provide implementations of all the Centered methods. 
  public void setCenter(double x, double y) { cx = x; cy = y; }
  public double getCenterX() { return cx; }
  public double getCenterY() { return cy; }
}