TreeMap.navigableKeySet().descendingIterator() sequence ?

[Alan Bateman]

Joshua Bloch wrote:
>
> Folks,
>
> While we're at it, here's another Collections bug discovered recently 
> by a Googler (Scott Blum).  The value of this expression should be false:
>
>     new IdentityHashMap().containsValue(null)
>
> Unfortunately, it's true.  Looking at the code for containsValue, it's 
> obvious what's wrong:
>
>     /**
>      * Tests whether the specified object reference is a value in this 
> identity
>      * hash map.
>      *
>      * @param value value whose presence in this map is to be tested
>      * @return <tt>true</tt> if this map maps one or more keys to the
>      *         specified object reference
>      * @see     #containsKey(Object)
>      */
>     public boolean containsValue(Object value) {
>         Object[] tab = table;
>         for (int i = 1; i < tab.length; i+= 2)
>             if (tab[i] == value)
>                 return true;
>
>         return false;
>     }
>
> Empty entries are masquerading as entries mapping to null.  The fix is 
> easy:
>
>             if (tab[i] == value)
>
> becomes:
>
>             if (tab[i] == value && tab[i -1] != null)
>
> (Recall that the null key (but not value) is proxied by NULL_KEY.)
>
>               Josh
>
I don't see this in the bug database so I've created the following so 
that it doesn't get lost:
  6691215: (coll) IdentityHashMap.containsValue(null) returns true when 
null value not present

-Alan.