[OT] surprising instance variable initialization exception behavior

Question

No real question here. Just something that caught me quite off guard. I thought I understood the object instantiation process pretty well, but there's clearly at least one significant gap in my knowledge.
Not surprisingly, the following gives "Error:Error:line (4)unreported exception java.lang.Exception; must be caught or declared to be thrown" for the new WTF2() line.
public class WTF1 {
  private final WTF2 wtf2 = new WTF2();
  WTF1() /* throws Exception */ {}
class WTF2 {
  WTF2() throws Exception {}
}Quite surprisingly (to me at least) if we uncomment "throws Exception" in the WTF1() c'tor declaration, the compiler is happy.
Reading [JLS 12.5 Creation of New Class Instances|http://java.sun.com/docs/books/jls/third_edition/html/execution.html#12.5], I can see that executing the instance initializers is step 4 of "the indicated constructor is processed to initialize the new object using the following procedure", so I guess I can see how executing the initializer can be considered "part of" executing the c'tor, and hence covered by its catch block. It just looks a little weird, and I always thought that the initializer executed before the c'tor, and had to catch checked exceptions.
Now that I've learned something, I'm ready to count this day as a win and head to the pub. :-)

Answer 1

BIJ001 wrote:
wtf2 is an instance variable, so (the appropriate copy) must be initialized in (every) constructor.Eh? No.
It's final, so therefore it must have it's value set by every normal completion of every ctor. But that's irrelevant to what I'm looking at. I'm talking about the fact that the declaration/initialization line complains or doesn't based on the throws clause of the c'tor.
I see now why it works that way, but I just thought the initializer execution was "outside of" the c'tor execution. I thought that if new WTF2() could throw a checked exception, I'd have to do something like we do for static initializers:
private final WTF2 wtf2;
  try {
    wtf2 = new WTF2();
  catch (Exception e) {
    throw some unchecked exception
}As it turns out, the initializer is executed "inside" the c'tor in a way I didn't expect.