Forewarned is forearmed As with other posts in this series, the above code is just an exercise that aims to showcase how easy it is to: Use Hazelcast embedded in one’s application Migrate from the standard java.util.concurrent API to the Hazelcast API This is by no way a showcase of the performance one can gain by using Hazelcast, especially given the limited size of the test data sets. Just to begin with, if you run tests, you’ll notice that the initialization of Hazelcast takes some time when the JVM starts. Then, the merge() implementation is not Hazelcast specific, and defaults to the one of ConcurrentHashMap : it’s not distributed-friendly. Perhaps such an optimization will be the subject of a future post.