ConcurrentMap.putIfAbsent(Object, Supplier)?

[Peter Levart]

Hi Philippe,

I think you are looking for Map.computeIfAbsent(K, Supplier) which was 
added to Map interface recently.

Regards, Peter

On 05/26/2013 01:22 PM, Philippe Marschall wrote:
> Hi
>
> I often find myself writing code like this:
>
> ConcurrentMap map = ...;
> Object value = map.get(key);
> if (value == null) {
>   Object newValue = expensiveComputation();
>   Object previous = map.putIfAbsent(key, newValue);
>   if (previous != null) {
>     value = previous;
>   } else {
>     value = newValue;
>   }
> }
> return value;
>
> This is quite error prone and tedious. If we had a method:
>
> V putIfAbsent(K key, Supplier<V> Supplier)
>
> it could be replaced with
>
> return map.get(key, () -> expensiveComputation());
>
> It could even be implemented with a default method assuming null 
> values aren't allowed which is the same as for the new #getOrDefault 
> default method.
>
> Cheers
> Philippe