Question

Possible Duplicate:
Tricky ternary operator in Java – autoboxing

We know that int roomCode = null; is not allowed by the compiler.

Then why the Code 1 doesn’t give a compiler error, when Code 2 does.

Code 1:

int roomCode = (childCount == 0) ? 100 : null;

Code 2:

int roomCode = 0;
if(childCount == 0) roomCode = 100;
else roomCode = null; // Type mismatch: cannot convert from null to int

Answer 1

I did a little debugging and found out that when evaluating

(childCount == 0) ? 100 : null;

the program calls the method valueOf of Integer to evaluate the null. It returns an Integer and as an Integer can be null (and not an int), it compiles. As if you were doing something like:

int roomCode = new Integer(null);

So it is related to autoboxing.