Re: LinkedList.clone() bug

[Bryce McKinlay <bryce at waitaki dot otago dot ac dot nz>]

Brad Fitzpatrick wrote:

> When testing my project built with gcj I found the output was different from
> the jar I'd built with Blackdown's bytecode compiler.  I traced it down to a
> minor bug in the gcj java library, as illustrated by this test case:

[...]

> Possible Patch ....
>
> --- gcc-3.0/libjava/java/util/LinkedList.java.orig Wed Jul 11 20:50:47 2001
> +++ gcc-3.0/libjava/java/util/LinkedList.java Wed Jul 11 20:51:11 2001
> @@ -466,14 +466,7 @@
>     */
>    public Object clone()
>    {
> -    LinkedList copy = null;
> -    try
> -      {
> - copy = (LinkedList) super.clone();
> -      }
> -    catch (CloneNotSupportedException ex)
> -      {
> -      }
> +    LinkedList copy = new LinkedList();
>      copy.size = 0;
>      copy.addAll(this);
>      return copy;
>
> Nothing about LinkedList implements clone() so I'm not sure what the
> previous code was trying to do.

Thanks for the bug report. The patch isn't correct in the presence of
subsclassing due to the use of new instead of clone - for example if you had
something like:

class MyLinkedList extends LinkedList{}

MyLinkedList l = new MyLinkedList();
Object clone = l.clone();

then the runtime type of the clone will be LinkedList instead of MyLinkedList
as would be expected. This is a mistake I've made in the past while working on
the collections classes ;-)

Instead, I think the correct fix is something like:

Index: LinkedList.java
===================================================================
RCS file: /cvs/gcc/gcc/libjava/java/util/LinkedList.java,v
retrieving revision 1.5
diff -u -r1.5 LinkedList.java
--- LinkedList.java     2000/12/04 10:20:00     1.5
+++ LinkedList.java     2001/07/13 03:18:11
@@ -474,7 +474,7 @@
     catch (CloneNotSupportedException ex)
       {
       }
-    copy.size = 0;
+    copy.clear();
     copy.addAll(this);
     return copy;
   }

I havn't tested this, however. Could you try it out and get back to me?

regards

  [ bryce ]