import java.util.Enumeration;
public interface ShoppingBasket {
    /*
     *   Adds an item into the shopping basket. If the item
     *   is already in the basket, the number of units of this item
     *   are added to the quantity of the existing item.
     *   @param newItem The item to be added.
     */
    public void addItem (Item newItem);

    /*
     *    Removes the given item from the shopping basket. The
     *    number of units in deletedItem are removed from the
     *    basket. E.g., if there are 10 units of the item in the
     *    basket, and we remove 3 units of the item, 7 units will
     *    remain.
     */
    public void removeItem (Item deletedItem);

    /*
     *    Returns an enumeration allowing the shopping list to be
     *    traversed.
     */
    public Enumeration elements ();

    /*
     *    Returns a version of the shopping basket in string form
     *    suitable for displaying.
     */
    public String toString ();
}