When running this:
public class WhatTheShoot {
public static void main(String args[]){
try {
throw null;
} catch (Exception e){
System.out.println(e instanceof NullPointerException);
System.out.println(e instanceof FileNotFoundException);
}
}
}
The response is:
true
false
Which was fairly stunning for me. I would have thought this would net a compile-time error.
Why can I throw null in Java, and why does it upcast it to a NullPointerException?
(Actually, I don’t know if it is an “upcast”, given I’m throwing null)
Aside from a really really stupid interview question (please nobody ask this in an interview) I cannot see any reason to throw null. Maybe you want to be fired, but that’s… I mean, why else would anyone throw null?
Fun fact IntelliJ IDEA 12 tells me that my line, e instanceof NullPointerException, will always be false. Which isn’t true at all.