AI migrated legacy COBOL programs to Java, bugs included

#1

Post by felineflock » Mon, Aug 03, 2026, 3:06 AM UTC

AI migrated legacy COBOL programs to Java, bugs included
arxiv.org

Re: AI migrated legacy COBOL programs to Java, bugs included

#2

Post by [deleted] » Mon, Aug 03, 2026, 5:08 AM UTC

[deleted]

Re: AI migrated legacy COBOL programs to Java, bugs included

#3

Post by madduci » Mon, Aug 03, 2026, 5:14 AM UTC

I remember a similar story shared this year at JAX2026 from the Sparkasse Group, they said they were using AI to migrate from COBOL, but they still were in the middle of the migration. Maybe they faced the same issues / problems? It seemed pretty zealous to me, that everything was working smoothly, but this article highlights the limitations

Re: AI migrated legacy COBOL programs to Java, bugs included

#4

Post by BigJono » Mon, Aug 03, 2026, 5:21 AM UTC

Yeah nah maybe fix the bugs before swapping the average COBOL dev for the average Java dev.

Re: AI migrated legacy COBOL programs to Java, bugs included

#5

Post by nicman23 » Mon, Aug 03, 2026, 5:29 AM UTC

BigJono wrote: post #4

Yeah nah maybe fix the bugs before swapping the average COBOL dev for the average Java dev.

sometimes if the bug exists for enough time it is intended behavior

Re: AI migrated legacy COBOL programs to Java, bugs included

#6

Post by surfingdino » Mon, Aug 03, 2026, 5:32 AM UTC

nicman23 wrote: post #5

BigJono wrote: post #4

Yeah nah maybe fix the bugs before swapping the average COBOL dev for the average Java dev.

sometimes if the bug exists for enough time it is intended behavior

Indeed, there may even be a whole lot of code that depends on it.

Re: AI migrated legacy COBOL programs to Java, bugs included

#7

Post by wwind123 » Mon, Aug 03, 2026, 5:40 AM UTC

surfingdino wrote: post #6

nicman23 wrote: post #5

Earlier quoted context omitted.

sometimes if the bug exists for enough time it is intended behavior

Indeed, there may even be a whole lot of code that depends on it.

Yeah. Bug-for-bug migration is a real thing in large code-bases in the industry. You want to replicate all behavior of the code regardless whether the behavior is a feature or a bug.

See Hyrum's Law: https://www.hyrumslaw.com/

Re: AI migrated legacy COBOL programs to Java, bugs included

#8

Post by tapland » Mon, Aug 03, 2026, 5:41 AM UTC

nicman23 wrote: post #5

BigJono wrote: post #4

Yeah nah maybe fix the bugs before swapping the average COBOL dev for the average Java dev.

sometimes if the bug exists for enough time it is intended behavior

Absolutely, and you'll have all kinds of fixes for the symptoms throughout the project.

COBOL isn't hard, the tooling around it on old systems are a pain though.

Re: AI migrated legacy COBOL programs to Java, bugs included

#9

Post by pacaro » Mon, Aug 03, 2026, 5:49 AM UTC

The largest test case was 4kloc.

There are hundreds of billions of lines of cobol in production.

The IRS alone has approx 160 cobol programs, averaging 230kloc each.

Re: AI migrated legacy COBOL programs to Java, bugs included

#10

Post by nkjoep » Mon, Aug 03, 2026, 5:50 AM UTC

surfingdino wrote: post #6

nicman23 wrote: post #5

Earlier quoted context omitted.

sometimes if the bug exists for enough time it is intended behavior

Indeed, there may even be a whole lot of code that depends on it.

Yep, and when it’s about money you don’t want any unexpected.