public class Sphere {
   double x,y,z,r;                // center and radius

   Sphere(double x, double y, double z, radius r) {
      moveTo(x,y,z);
      resize(r);
   }

   public void moveTo(double x, double y, double z) {
      this.x = x;
      this.y = y;
      this.z = z;
   }

   public void resize(double r) {
      if (r > 0)
         this.r = r;
      else
         r = 0;
   }

   public double volume() {
      return (4 * Math.PI * Math.pow(r,3))/3
   }

   public boolean inside(double x, double y, double z) {
      return (distanceToCenter(x,y,z) < r);
   }

   double distanceToCenter(double x, double y, double z) {
      return Math.sqrt(Math.pow(x - this.x, 2) +
                       Math.pow(y - this.y, 2) +
                       Math.pow(z - this.z, 2));
   }

   public String toString() {
      return ("sphere at (" + x + "," + y + "," + z + ") with radius " + r);
   }
}