README.txt

add a method set(int n, Object o) which replaces the nth element in the list

assignment.java

public class Assignment {
	public static void main(String[] args) {
		LinkedList list = new LinkedList();
		for(int i = 4; i > 0; i--) {
			list.addFirst(i);
		}
		list.print();
		System.out.println("The size is: " + list.size() + ".");
		list.set(2, 66);
		list.print();
	}
}

LinkedList.java

public class LinkedList {
	private class ListElement {
		private Object el1;
		private ListElement el2;

		public ListElement(Object el, ListElement nextElement) {
			el1 = el;
			el2 = nextElement;
		}

		public ListElement(Object el) {
			this(el,null);
		}

		public Object first() {
			return el1;
		}

		public ListElement rest() {
			return el2;
		}

		public void setFirst(Object value) {
			el1 = value;
		}

		public void setRest(ListElement value) {
			el2 = value;
		}

	}

	private ListElement head;
	private int count;

	public LinkedList() {
		head = null;
	}

	public void addFirst(Object o) {
		head = new ListElement(o,head);
		count++;
	}

	public Object getFirst() {
		return head.first();
	}

	public Object get(int n) {
		ListElement d = head;
		while(n>0)
		{
			d = d.rest();
			n--;
		}
		return d.first();
	}

	public void print() {
		System.out.print("(");
		ListElement d = head;
		while(d != null)
		{
			System.out.print(d.first().toString() + " ");
			d = d.rest();
		}
		System.out.println(")");
	}
	
	public int size() {
		return count;
	}
	
	public void set(int n, Object o) {
		// first, try to find n-1 and n+1; let's call them nMin and nPlus
		ListElement nMin = null;
		ListElement nPlus;

		if (n > 0) {
			// if we're not setting element with index 0, we can run through the linked list
			nMin = head;
			while (n-1 < 0) {
				nMin = nMin.rest();
				n--;
			}
			// and we can use n-1 to find n+1
			nPlus = nMin.rest().rest()			
		} else {
			// Otherwise, n+1 is really just element with index 1, or head.rest()
			// in this case, nMin doesn't exist, so we let it be 0
			nPlus = head.rest();
		}

		// turn this element into a ListElement and make it point to n+1
		// because we're going to insert this element between n-1 and n+1
		ListElement thisObject = new ListElement(o, nPlus);
		
		// if nMin is null, that means we're making a new head, so just assing the new object to the head
		if (nMin == null) {
			head = thisObject;
		} else {
			// otherwise, make n-1 point to this element
			nMin.setRest(thisObject);
		}

		// and we're done. obviously, this could fail in a number of ways, most likely nullpointer exceptions because we're not sanitising the "n" parameter at all. but whatever.
	}
}