New to Java

I have a class(arrayList) and an Interface(ListInterface) and I'm making a new class(Set)

I'm stuck on the constructor

	public class Set {

	private ListInterface data;   // The ADTList to hold the set elements. 
	
	/**
	 * Initializes an empty set.
	 */
	public Set() 
	{
		data = new ListInterface;
	}

this gives the error that it cannot instantiate the type ListInterface, and it doesn't work without the parentheses either.

I dont know what to do, any help?