public class DSLinkedStack<T> implements DSStackInterface<T> 
{
  private DSLLNode<T> top;
 
  public DSLinkedStack()
  {
    top = null;
  }

 
  public void push(T element)
  {
    top = new DSLLNode<T>(element, top);
  }
 
  public void pop() throws StackUnderflowException
  {
    if (!isEmpty())
      top = top.getNext();
    else
      throw new StackUnderflowException("Top attempted on empty stack.");
  }
 
  public T top() throws StackUnderflowException
  {
    if (!isEmpty())
      return top.getData();
    else
      throw new StackUnderflowException("Top attempted on empty stack.");
  }
 
  public boolean isEmpty()
  {
    return (top == null);
  }
  
  public boolean isFull()
  {
    // The Link-based stack is never full.
    return false;
  }
}