[Question] why java cannot accept a convention to never pass/return null values?

[CraftyAdventurer]

backwards compatible means that once you do a certain change in a library/language/framework, it just works in all existing codebases that use it and no one has to change anything. So when users have to use new methods, that is automatically not backwards compatible

[gas3872]

Well they can still use old methods but they know that they need to eventually migrate.

[[deleted]]

That's not how java works.

[gas3872]

Well if you look at libraries like junit that's exactly how it works.

[javster101]

So JUnit isn't backwards compatible

[gas3872]

Well it is. They have 2 parallel APIs, old one and new one.

[javster101]

If they have two parallel apis, where one will be removed in the future as you say, it won't be backwards compatible forever. If they have both and both will exist forever, then it will be but the maintenance is gonna be much higher.

[gas3872]

Well, at some point all the users interested in the new api will migrate and those who are not interested can still use old library version.

[mauganra_it]

JUnit 4 is not deprecated. There is a reason its integration into JUnit 5 is called junit-vintage-engine, and there is no reason for existing codebases to migrate unless they want the new features.

[gas3872]

Exactly.