implementato nodeposition con to string e reverse. aggiunto copyright

position/DNode.java

@@ -0,0 +1,36 @@
+package position;
+import  exceptions.*;
+/**
+ * A simple node class for a doubly-linked list.  Each DNode has a
+ * reference to a stored element, a previous node, and a next node.
+ * 
+ * @author Roberto Tamassia
+ */
+//Copyright (c) 2003 Brown University, Providence, RI
+//Additional modifications and methods by xgiovio
+
+public class DNode<E> implements Position<E> {
+  private DNode<E> prev = null;
+    private DNode<E> next = null;
+  private E element = null;
+
+  public DNode(DNode<E> newPrev, DNode<E> newNext, E elem) {
+    prev = newPrev;
+    next = newNext;
+    element = elem;
+  }
+
+  public E element() throws InvalidPositionException {
+    if ((prev == null) && (next == null))
+      throw new InvalidPositionException("Position is not in a list!");
+    return element;
+  }
+
+  public DNode<E> getNext() { return next; }
+  public DNode<E> getPrev() { return prev; }
+
+  public void setNext(DNode<E> newNext) { next = newNext; }
+  public void setPrev(DNode<E> newPrev) { prev = newPrev; }
+  public void setElement(E newElement) { element = newElement; }
+}
+