public void addItemToShoppingCart(ShoppingCartItem item){
  if (item == null) {
    throw new InvalidParameterException("Error adding ShoppingCartItem, it may not be null");
  }
  shoppingCartItems.add(item);
}

public void addItemToShoppingCart ( ShoppingCartItem item ) { if ( item == null ) { throw new InvalidParameterException ( "Error adding ShoppingCartItem, it may not be null" ) ; } shoppingCartItems . add ( item ) ; }
add a shoppingcartitem to the shoppingcart
