Yes, the final example code reads reasonably nicely, but alas -- unless ConcurrentHashMap.merge() has been rewritten since Java 8 time -- it is definitely not a

Yes, the final example code reads reasonably nicely, but alas -- unless ConcurrentHashMap.merge() has been rewritten since Java 8 time -- it is definitely not as performant as the author appears to think it is since the actions will be contained in a fairly long synchronized block. This is not to say the code is bad, but you can't get around that. Somewhat surprisingly, the code the author pooh-poohs is actually more performant (although it's better if the test is for the presence of the key rather than the "putIfPresent/computeIfAbsent combination) because the JVM will properly optimize a membership test (in keyset) and the use of a ternary expression makes the action clear.