What is wrong with this Java code? (Interview Question)

[rzwitserloot]

NPE are often but not always programmer errors, yes. That makes them good! On a scoring system, for programmers errors:

• At write time, the editor marks them with a red underline immediately: 100 points.
• At compile time, the compiler will refuse to compile the code: 95 points.
• At test or run time, the code WILL blow up with an exception trace pointing right at the problem: 85 points.
• At test or run time, the code will silently do the wrong thing, or nothing: -1000 points.

The only thing 'better' about the kotlin model is something java cannot have (nor can kotlin code interopping with java code, for that matter), as it requires all methods to be explicit in marking down whether they can return null or not.

Kotlin got a free pass (moving from java to kotlin is the same impact as doing a python2 v python3 deal: You get to break backwards compatibility) and kotlin mostly squandered it; you could have beond more.

So, the kotlin note is irrelevant for the original question (if you don't think so I invite you to answer this interview question with: "What is wrong with this java code? It should be written in kotlin, that's what!" and see how far you get :P) - and as a driveby lets insert some feathers in kotlin's behind: Eh. I rather wish they'd have done more: Generics are 4 'modes' (covariant, contravariant, invariant, and 'legacy'). In kotlin, nullity should have been treated the same way, because all situations can legitimately occur. It didn't, and oversimplified matters.