Fun story: back in 2009 at the jvm language summit, Thomas Wuerthinger demo’d full hotswap.

Method signature changes, class hierarchy, all of it.

He wasn’t a sun employee at the time and the sun folks kept telling him what he was doing was impossible. We ended up using his stuff, the dcevm, internally for a long time.

He was eventually hired by sun/oracle to work on other stuff and Java still doesn’t have proper hotswap.

That’s the tech world for you.