I have this method in City class. It should create a new city based on the object which the method is applied to: public City newCity(string newCityName, int dX, int dY) { City c=new City(this); //based on a constructor : City(City c){} c.CityName=newCityName; c.NoOfNeighborhoods=1; c.NumOfResidents=0; c.CityCenter.Move(dX,dY); return c; } CityCenter is of type "Point" which has two fields - x,y. the Move method in Point class is ment to change the CityCenter location. It looks like this: public void Move(int dX, int dY) { this.X = x + dX; this.Y = y + dY; } What happens is that the new object,c and the existing City object are both changed. I think that "this" modifier works on the existing object too... How can I take advantage of the Move method without causing this behavior? Note: this is a closed API, so I can only add private methods to the project.