Thread: Comparing Generics; Quick Question

Hi,

I'm making a linked list implementation of a polynomial. My node, is a generic type with 2 elements; Coefficients and Powers. However, now i need to compare 2 nodes to see which has the largest power, so that it is placed first (canonical polynomial form). Unfortunately, it seems to be having a problem comparing these generics, i'm a little bit lost to be honest but i feel like its a simple solution.

This is the part thats giving me trouble (its within the add method: if (temp.getElement2()> q.getElement2()){

The error states: The operator > is undefined for the argument type(s) java.lang.Object, java.lang.Objec


Here is my code:

 
class Polynomial
{
	Node head;	
 
	Polynomial()
	{
		head = new Node(null,null);
	}
 
//add new nodes into the polynomial
 
	public void add(int coef, int power)
	{
 
		Node temp = new Node(coef, power);		
 
		if (head == null)
			head = temp;
		else {
			Node p = null;
			Node q = head;
 
//insert in front if exponent is higher
 
			if (temp.getElement2()> q.getElement2()){
			temp.setNext(head);
			head = temp;
			}
//insert at middle or end
                        else {
 
				while (q != null && q.getElement2() > temp.getElement2()){
					p = q;
					q = q.getNext();
				}
				p.setNext(temp);
				temp.setNext(q);
			}
		}
 
	}	
 
//to string		
	public String toString()
	{
		Node current = head.getNext();
		String output = "";
		while(current != null)
		{
			output += "(" +current.Element1.toString() + "," + current.Element2.toString() + ")";
			current = current.getNext();
		}
		return output;
	}
 
//node class
	class Node<E> 
	{
		E Element1, Element2;
		Node<E> next;
 
		public Node(E Element1,E Element2)
		{			
			this.Element1 = Element1;			
			this.Element2 = Element2;
			next = null;
		}
 
		public Node getNext()
		{
			return next;
		}
 
		public void setNext(Node next)
		{
			this.next = next;
		}
 
		public E getElement1() {
			return Element1;
		}
 
		public void setElement1(E element1) {
			Element1 = element1;
		}
 
		public E getElement2() {
			return Element2;
		}
 
		public void setElement2(E element2) {
			Element2 = element2;
		}
 
 
	}
}

Please help, im nearly done with this project

thanks in advance

The error pretty much explains it all. You can't use arithmetic operators on Objects. You can use them on Integers or Doubles or Floats, only because of auto-unboxing, but you can't use them on generics that could be a different kind of Object.

To further explain why, what would happen if I passed in JTable as the generic argument to your Node class? How do you compare two JTables for < or > ?

Well, you have to come up with rules to determine what "largest" means for different Objects. When is one JTable greater than another JTable?

Are you sure Node is supposed to be a generic class? I don't see you using it in a generic way, and it's complicating your comparisons. Doesn't make a ton of sense.

Originally Posted by clydefrog

no it doesnt have to be generic, i just though it would be easier. You suggest i change the node to just work with ints?

What happened when you tried? Are you supposed to be able to use decimals?