XOM API for Processing XML with Java

[Remko Popma <remko.popma AT azzurri.jp>]

> The ParseException problem was easily found by switching to Java 1.4 
> for the compile. What I don't understand is why the change was 
> necessary. Shouldn't an overriding method be allowed to return a 
> subclass of the return type of the original, overridden method? In 
> this case, a ParseException is a Throwable, after all. Any idea 
> what's going on here?

The java language spec doesn't allow a different return type 
when overriding or hiding methods. It doesn't matter whether the return
type in the overriding method is a subclass of the return type of the 
overridden method or not.

From: 8.4.6.3 Requirements in Overriding and Hiding
(http://java.sun.com/docs/books/jls/second_edition/html/classes.doc.html#227965)

"If a method declaration overrides or hides the declaration of another 
method, 
then a compile-time error occurs if they have different return types (...)"


(see also:
8.4.6.4 Inheriting Methods with the Same Signature
http://java.sun.com/docs/books/jls/second_edition/html/classes.doc.html#227941)


I don't know if this could be one of the reasons for this rule, but
the spec also says that it breaks binary compatibility to change the result 
type of a method.
(http://java.sun.com/docs/books/jls/second_edition/html/binaryComp.doc.html#45208)