public interface ListInterface
{
    // makes the list contain no items
    public void clear();

    // add item at start of list
    public void add (Object item);
    
    // add item at given position
    // generates an IllegalPositionException if position is invalid
    public void add (Object item, int position);
    
    // remove the item that exists at the given position
    // generates an IllegalPositionException if position is invalid
    public void remove (int position);
    
    // remove first occurrence of item in the list
    // if item does not exist, do nothing
    public void remove (Object item);
    
    // remove all occurrences of item in list
    // if item does not exist, do nothing
    public void removeAll (Object item);
    
    // returns the item at the given position
    // generates an IllegalPositionException if position is invalid
    public Object viewItem(int position);
    
    // place the list into ascending order
    public void sort();
    
    // print all items in the list
    public String toString();
    public void print();
    
    // return the number of items in the list
    public int size ();

}