Slightly deceiving error message on Collectors.toMap

[Brian Goetz]

Rewinding:

*Obviously*, it would be best if the colliding *key* were printed.

Michael already observed that, at the point where the error is detected, 
the key is not easily available.

So the best fallback is to say "some key which I can't tell you mapped 
to values V1 and V2", providing the user all the information we have in 
the hopes of helping the user.

On 4/17/2014 12:37 PM, Michael Nascimento wrote:
> On Thu, Apr 17, 2014 at 1:04 PM, Peter Levart <peter.levart at gmail.com> wrote:
>> But the two values are the same (if the key->value mapper function *is* a
>> function), aren't they?
>
> No, for example:
>
> Stream.of(1, 1).collect(toMap(identity(), i -> Math.random()));
>
> Another example would be something like:
>
> cities.stream().collect(toMap(City::getName, identity()));
>
> If there are cities from different states in the collection, their
> names might collide. Printing both values (with a decent toString)
> will help developers to figure out their mistake.
>
> Regards,
> Michael
>