Linked Data Structures - Absolute Java - page 825

The copy constructor is defined by using the private helping method copyOf to
create a copy of the list of nodes. Other details of the copy constructor and the clone
method are done in the standard way.
Although the copy constructor and the clone method each produce a new linked
list with all new nodes, the new list is not truly independent because the data objects
are not cloned. See the Pitfall “The clone Method Is Protected in Object ★ ” for
a discussion of this point. One way to fix this shortcoming is discussed later in the
Programming Tip entitled “Use a Type Parameter Bound for a Better clone .”

Exceptions ★
A generic data structure, such as the class LinkedList in Display 15.12 , is likely
to have methods that throw exceptions. Situations such as a null argument to
the copy constructor might be handled differently in different situations, so it is
best to throw a NullPointerException if this happens and let the programmer
who is using the linked list handle the exception. This is what we did with the
copy constructor in Display 15.12 . A NullPointerException is an unchecked
exception, which means that it need not be caught or declared in a throws clause.
When thrown by a method of a linked list class, it can be treated simply as a run-
time error message. The exception can instead be caught in a catch block if there is
some suitable action that can be taken.

Display 15.12 A Copy Constructor and clone Method for a Generic Linked List (part 1 of 3)

1 public class LinkedList3<T> implements Cloneable
2 {
3 private class Node<T>
4 {
5

This copy constructor and this clone
method do not make deep copies. We
discuss one way to make a deep copy in the
Programming Tip “Use a Type Parameter
Bound for a Better clone .“

private T data;

6 private Node<T> link;

7 public Node( )
8 {
9 data = null ;
10 link = null ;
11 }

12 public Node(T newData, Node<T> linkValue)
13 {
14 data = newData;
15 link = linkValue;
16 }
17 } //End of Node<T> inner class

(continued)