Am 07.09.2010 10:50, schrieb David Holmes:
Jeroen Frijters said the following on 09/07/10 17:59:
David Holmes wrote:
The fact that Object.clone() is implemented via a native call into
the VM is simply an implementation detail.
That's not what we're talking about. We're talking about the fact
that arrays (appear to) have a *public* clone method. The argument is
about the return type[1] of this method: according to the JLS it is
X[], but according to the VMSpec it is Object. This difference is
fine, but I'm arguing that the JLS fiction should be in the JLS, not
in the Object.clone() documentation.
I don't see where the VMSpec says anything about cloning ... but that aisde. I hadn't realized
that the JLS states that arrays override Object.clone() rather than inheriting it - it would have
been simpler to cover the array and non-array cases in Object.clone().
As it stands there is no actual API doc in which to put this information, so we really have no
choice but to put it Object (having it only in the JLS is inadequate). That said I would call it
out explicitly in its own paragraph, something like:
"All array types, X[], are considered to implement Cloneable and to override this method to return
a new X[] containing the same elements as the original."
+1
This statement, which describes the compile-time behaviour, more belongs to the
JLS.
Jeroen, do I understand you right, that you agree with me? :
In javadoc of class Object we should better note for the run-time behaviour. In
other words:
As array types clone method is considered to be silently overridden in covariant way, method clone
of an array object X[] returns a new array of class X[], filled with it's original's content.
Additionally we could note in javadoc of method clone of class Object:
If overriding the clone method, it is recommended to use the covariant return type to avoid the need
of casting in the calling code. Example:
class MyClass {
@override
public MyClass clone() {
MyClass clone = (MyClass)super.clone();
clone.doSomeMoreWork();
return clone;
}
}
-Ulf
