public void addItem(CartItem item)  throws Exception {
	if(item == null) {
		//...(throw an exception)
	}

	if(item.getBookOrCD().equals("B")) {  // if the item is a book
		boolean found = false;
		for(int index=0; index < BookList.size(); index++) {
			CartItem temp = (CartItem)BookList.elementAt(index);
			if(  //... (if the item to be added is the same as the temp item)  {
				found = true;  // the cart has another copy of the same item
				// ...(set the quantity for temp to quantity + 1)
                                // ...(store the updated item in the vector)
                                // ...(update the total price by adding the unit price of 
                                //     current item multiplied by the quantity of such items 
                                //     you are adding in the cart right now)
				break;
			}
		}

		if(!found){   // if the cart did not have another copy of the same item
			// ...(add the item to the vector which is a list of books)
			// ...(update the total price of all items in the cart)
		}
	}
	else { // if the item is a CD
		//...(similar implementation for the case of a CD)
                //...
                //...
                //...
                //...
                //...
                //...
			
	}
}