No compiler error when assigning null to a primitive with ? :

Question

In 5.0, the statement
int a = true ? null : 0;
does not produce a compiler error. In 1.4 it produced an error stating "Incompatible conditional operand types int and null". I understand that auto-boxing complicates the compiler's job here, but isn't it still possible for the compiler to error on this statement?

Answer 1

That's perfectly legit in 1.5 because of autoboxing.
The compiler looks at the expression
true?null:0and needs to determine the type produced by it. 0 can be autoboxed to an Integer and null is a valid Integer value, so that expression produces an Integer.
Then, it tries to auto-unbox the Integer to assign it to the primitive int. And the same thing happens as always happens when you try to auto-unbox null: you get a NullPointerException. :)