Constructors that throws Exception.

[Alton Hernandez]

While doing Dan's mock exam I came across this question:

class A {
A() throws Exception {} // 1
}
class B extends A {
B() throws Exception {} // 2
}
class C extends A {} // 3

Which of the following statements are true?
a. Compiler error at 1.
b. Compiler error at 2.
c. Compiler error at 3.
d. None of the Above
ANS: c

I answered d thinking that since an overriding method does not need to declare any throws clause(even if the overridden method has one), then it must be the same for constructors.
I understand that constructors are not like methods, and the JLS did specified that

JLS 8.8.7
A default constructor has no throws clause.
It follows that if the nullary constructor of the superclass has a throws clause, then a compile-time error will occur.

But so far, I don't see any reason why the rules have to be any different for constructors? Why does the rule "may not be declared to throw more checked exceptions" not applicable to constructors?
Thanks.

[Alton Hernandez]

OK, let me try answering my own question.
Constructors are called in successions i.e. the subclass will call its superclass' constructors, and so forth. Now if the call to the constructor is implicit, obviously you cannot put it inside a try/catch clause. And if the call is explicit, you also cannot put it inside the try/catch clause because of the provision that the first statement must either be super() or this(). So now if the superclass constructor throws an exception, the subclass constructor has no choice but to throw it also. So that is why it has to declare it.
Am I right on this one?

[Marlene Miller]

Hi Alton. That is the same reasoning process I followed when I tried to explain it to myself. I looked for confirmation in the JLS and other places and I could never find any.

[Ross Goldberg]

Your description was the first thing that popped in my mind and seems fully logical. After all, you have to handle or declare and when you're getting to class C, you're neither handling or declaring. Sounds like an explosion waiting to happen...
Ross

[Marlene Miller]

I found something!

If an exception is thrown during the construction process, the new expression terminates by throwing that exception--no reference to the new object is returned. As an explicit constructor invocation must be the first statement in a constructor body, it is impossible to catch an exception thrown by another constructor.
(If you were allowed to catch such exceptions it would be possible to construct objects with invalid initial states.)

In my favorite Java book, The Java Programming Language, 3.2.1 Constructor Order Dependencies
[ August 05, 2003: Message edited by: Marlene Miller ]