Writing clone() method for LinkedList

**vluong** · October 26th, 2009, 06:51 PM

Hello, JPF. I am trying to implement my own LinkedList and the clone method I have written doesn't seem to work. Can anyone tell me what I did wrong? Thanks!

Okay, this is what I have in my tester:

import java.util.*;
public class OurLinkedListTest
{  public static void main (String [] args)
   {  try
     {
      OurLinkedList <String> myList = new OurLinkedList<String>();
      myList.add("A");
      myList.add("B");
      myList.add("C");
      myList.add("B");
      myList.add(2, "X");
      myList.addFirst("Y");
      myList.addLast("Z");
      OurLinkedList <String>cloned = (OurLinkedList<String>)myList.clone();
   }
   catch(IllegalStateException e)
   {  System.out.println("Rule #2 is violated.");
   } 
}
}

public Object clone()
  {
     LinkedList<String> clone = new LinkedList<String>();
     for (int i=0; i<size; i++)
     {
        clone.add(get(i));
     }
     return clone;
  }

**literallyjer** · October 26th, 2009, 07:02 PM

Why does your clone method repeatedly (assuming size is greater than 1) add "A" into the cloned list and not the values of the list it is cloning?

**vluong** · October 26th, 2009, 07:05 PM

literallyjer, the "A" are just used for testing and I forgot to change it before posting (it's been changed). I get this error:

Exception in thread "main" java.lang.ClassCastException: java.util.LinkedList
at OurLinkedListTest.main(OurLinkedListTest.java:14)

**literallyjer** · October 26th, 2009, 07:09 PM

I am assuming that line 14 is this:

OurLinkedList <String>cloned = (OurLinkedList<String>)myList.clone();

If that's the case, then you are trying to cast a LinkedList into your OurLinkedList. Look closer at your clone method. You are cloning an OurLinkedList into a LinkedList and then trying to cast the LinkedList into an OurLinkedList.

**vluong** · October 26th, 2009, 07:15 PM

Thanks a bunch, literallyjer! It works now!

**literallyjer** · October 26th, 2009, 07:19 PM

You are very welcome :-)

**Json** · October 27th, 2009, 08:41 AM

You should also implement Cloneable.

// Json

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