There are actually companies (very few) that work with migrating large cobol code bases to java, in a automated manner. And it costs a lot, hundreds of millions and it takes a couple of years. They ensure that the cobol and java execution is doing the same thing. So it works, but it’s shit. Many do this because it’s hard to find cobol developers and the cost of IBM mainframes.

Anyways the code turns into cobol style in Java, horrible and hard work with, would never like to maintain it.