Linked Data Structures - Absolute Java - page 827

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

56 private Node<T> copyOf(Node<T> otherHead)
57 {
58 Node<T> position = otherHead; //moves down other's list.
59 Node<T> newHead; //will point to head of the copy list.
60 Node<T> end = null ; //positioned at end of new growing list.

Invoking clone with position.data would be illegal.

61 //Create first node:
62 newHead =
63 new Node<T>(position.data, null);
64 end = newHead;
65 position = position.link;

66 while (position != null)
67 { //copy node at position to end of new list.
68 end.link =
69 new Node<T>(position.data, null);
70 end = end.link;
71 position = position.link;
72 }

Invoking clone with position.data
would be illegal .

73 return newHead;

74 }
75 }

PITFALL: The clone Method Is Protected in object ★

When defining the copy constructor and clone method for our generic linked list
(Display 15.12), we would have liked to have cloned the data in the list being copied.
We would have liked to change the code in the helping method copyOf by adding
invocations of the clone method as follows:

newHead =
new Node((T)(position.data).clone( ), null );
end = newHead;
position = position.link;

while (position != null )
{ //copy node at position to end of new list.
end.link =
new Node((T)(position.data).clone( ), null );
end = end.link;
position = position.link;
}

This code is identical to code in copyOf except for the addition of the invocations of
clone and the type casts. (The type casts are needed because Java thinks clone returns
a value of type Object .)

(continued)