ConcurrentMap.putIfAbsent(Object, Supplier)? (original) (raw)

Peter Levart peter.levart at gmail.com
Sun May 26 11:25:34 UTC 2013

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 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

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