implementato nodeposition con to string e reverse. aggiunto copyright

exceptions/BoundaryViolationException.java

@@ -0,0 +1,18 @@
+package exceptions;
+
+/**
+ * Signals that the boundaries of a data structure have been illegally
+ * traversed (e.g. past the end of a list).
+ * @author Roberto Tamassia
+ */
+//Copyright (c) 2003 Brown University, Providence, RI
+//Additional modifications and methods by xgiovio
+
+public class BoundaryViolationException extends RuntimeException {
+  public BoundaryViolationException(String message) {
+    super (message);
+  }
+    public BoundaryViolationException() {
+        super ("BoundaryViolationException");
+    }
+}

exceptions/EmptyListException.java

@@ -0,0 +1,18 @@
+package exceptions;
+/**
+ * Thrown when a list cannot fulfill the requested operation because
+ * it is empty.
+ * @author Roberto Tamassia
+ */
+//Copyright (c) 2003 Brown University, Providence, RI
+//Additional modifications and methods by xgiovio
+
+
+public class EmptyListException extends RuntimeException {
+  public EmptyListException(String message) {
+    super (message);
+  }
+    public EmptyListException() {
+        super ("EmptyListException");
+    }
+}

exceptions/InvalidPositionException.java

@@ -0,0 +1,21 @@
+package exceptions;
+/**
+ * Thrown when a position is determined to be invalid.
+ * @author Roberto Tamassia, Michael Goodrich
+ */
+//Copyright (c) 2003 Brown University, Providence, RI
+//Additional modifications and methods by xgiovio
+
+
+public class InvalidPositionException extends RuntimeException {  
+  public InvalidPositionException(String err) {
+    super(err);
+  }
+
+  public InvalidPositionException() {
+      super("Invalid Position");
+
+  }
+
+}
+