having worked with kotlin for about a year, I’m personally thinking of switching the project back to java slowly, kotlin only real killer feature is treating null like java treats other types, and requiring it to be specifically managed. The rest of it… either isn’t a significant improvement, or since java 8/11+ just isn’t as good as what java itself supplies. SAM detection isn’t as good and I find myself often writing more verbose code than I would in java. method signatures are usually longer than they are in java because of the fun, and : noise. Intellij doesn’t behave to the same quality when writing kotlin as it does with Java. Most of the features I thought kotlin was going to bring simply turned out to be non-existant (like real trait support). If java got the improved explicit null handling I would jump back in a heartbeat. My 2 cents anyways.