The List: 3/27

• A list is an item followed by a list, OR
• A list is empty.

Some simple operations:

• To add a new-item to the end of a list: if the list is empty, say the list contains the new-item following by a list that is empty. Otherwise, add the item to the rest of the list.
• To remove the first item from a list: if the list is empty, return null, otherwise, set the first item to the second item, and the rest of the list to the second item's rest of list, and return the old first item.
• To count the number of items on the list: if the list is empty, it has zero items, otherwise it has 1 plus the number of items on the rest of the list.
• To return the item at the ith list item: if i is zero, then return the item, otherwise return the item at i-1th item in the rest of the list.

public class List 
{
    public Object item;
    public List next;
    

    public List() 
    {
	item = null;
	next = null;
    }

    public void add(Object obj) 
    {
	if (next == null) {
	    next = new List();
	    item = obj;
	} else {
	    next.add(obj);
	    
	}
    }

    public Object remove()
    {
	Object o = item;

	if (next != null) {
	    item = next.item;
	    next = next.next;
	}
	return o;
    }


    public boolean isEmpty() 
    {
	return next == null;
    }
    
    
    public int size() 
    {
	if (isEmpty())
	    return 0;
	else return 1 + next.size();
    }
    

    

    public Object get(int i)  
    {
	if (isEmpty()) {
	    throw new IndexOutOfBoundsException();
	}
	
	if (i == 0) {
	    return item;
	} else
	    return next.get(i-1);
    
    }

    static public void main(String args[]) 
    {
	List l = new List();
	l.add("A");
	l.add("B");
	l.add("C");

	System.out.println(l.size());
	System.out.println(l.get(2));
	System.out.println(l.remove());
	System.out.println(l.remove());
	System.out.println(l.remove());
	System.out.println(l.remove());	

    }
}