Comparator

[Henry Jen]

Or use the new static method,

.sorted(Map.Entry<String, Integer>.comparingByValue())

Cheers,
Henry

On Jul 15, 2013, at 9:09 AM, Maurizio Cimadamore <maurizio.cimadamore at oracle.com> wrote:

> On 15/07/13 16:53, Marc Petit-Huguenin wrote:
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>> Hi,
>> 
>> I am trying to use a comparator on a Map.Entry<String, Integer> stream, and I
>> am not sure why this does not compile:
>> 
>> .sorted(Comparator.comparing(Map.Entry::getValue))
> This is as expected - the method reference Map.Entry is defined on a 
> generic class with unknown parameter types (some Map<K, V>) - therefore 
> the compiler needs the info from the target (in a top-down way) in order 
> to decide what the method reference looks like. But the target type info 
> is incomplete as it depends on inference variables on its own.
> 
> So the compiler ends up applying a simpler (arity-based only) check 
> during overload resolution - which means the compiler can't really pick 
> the right comparing() method ahead of the target-type.
> 
> A shorter way to get this to compile should be this:
> 
> .sorted(Comparator.comparing(Map.Entry<String, Integer>::getValue))
> 
> 
> Let me know if that works for you.
> 
> Maurizio
>> 
>> error: reference to comparing is ambiguous
>> error: incompatible types: Cannot instantiate inference variables T because of
>> an inference loop
>> 
>> (interestingly the second error was not present when using a build from last week)
>> 
>> These two compile:
>> 
>> .sorted(Comparator.comparing((ToIntFunction<Map.Entry<String,
>> Integer>>)Map.Entry::getValue))
>> 
>> .sorted(Comparator.comparing((Map.Entry<String, Integer> entry) ->
>> entry.getValue().intValue()))
>> 
>> Thanks.
>> 
>> - -- 
>> Marc Petit-Huguenin
>> Email: marc at petit-huguenin.org
>> Blog: http://blog.marc.petit-huguenin.org
>> Profile: http://www.linkedin.com/in/petithug
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