Care to elaborate on this a bit? Some details would've been useful rather than just a "no u" comment.
You want to translate 'idiomatic COBOL soup' which has been added to over decades into clean structured (possibly OOP) code covered by a robust library of tests.
COBOL is used still for far more reasons than technical debt, there is good reason for the language and I doubt Java is even capable of replacing it. Even if an AI could write a 100% perfect Java version of COBOL, Java would fall flat on its face. COBOL and other languages like it are very performant languages, optimized over more than a half century.