I'm a bit surprised to see those examples, because there's nothing really new here. These are typical beginner pitfalls and have been there for at least a decade or more. Or maybe it's because I learned java in the late 90s and later used it for J2ME, and then using things like StringBuilder (StringBuffer in the old days) were almost mandatory, and you would be very careful trying to avoid unnecessary object allocations.

I remember writing Java for our introductory programming course at university around 2010. I was already familiar with object oriented programming in PHP at the time, so I just wrote the Java code like I would write PHP. I was absolutely astounded at the poor performance of the Java app. I asked one of our tutors and I can still remember him looking at the code and saying something along the lines of ”oh, you’re instantiating objects in a loop, that’s obviously going to be slow”. Like, what? If I can do this performantly in freakin PHP, how can Java, the flagship of OOP, not have fast instantiation of objects? I’m still shaking my head thinking about it.