Re: this reference in Java constructors
On Oct 29, 1:26 pm, Eric Sosman <Eric.Sos...@sun.com> wrote:
Lew wrote:
Eric Sosman wrote:
It's fairly easy to get an arbitrary
amount of code executed *before* the superclass' constructor
runs, as in
class Counterexample extends HasBoolConstructor {
Counterexample() {
super(boolMethod());
}
private bool boolMethod() {
[...]
return pearTree.add("Partridge");
}
private static final HashSet<String> pearTree =
new HashSet<String>();
}
Lew wrote:
In addition to the obvious dangers here that you've already discussed=
,
the instance-level access to a static structure is problematic. Th=
is is
a well-crafted example of code idioms to avoid.
Eric Sosman wrote:
Okay, it was a whimsical example -- but maybe because of
whimsy I'm about to learn something I didn't know. Why is it
"problematic" to access a static element from non-static code?
That isn't what I said.
class Problematic {
public void announce() {
System.out.println("Problematic?");
}
}
That's not the same at all. What I said is that "the access ... is
problematic", that is, the particular one under discussion, not just
any access.
The access to which I referred was an instance-level write to a static
memory structure. Your new example is a write to a stream, thus ther=
e
is no further state to observe. Apples and oranges.
System.out isn't static? PrintStream has no observable stat=
e?
In your first example the access is problematic because it isn't
thread safe. That is not true for your second example.
Red herring. Use Collections.synchronizedMap() on it if you=
like:
Now it's thread-safe, but still static. What's "problematic?"
Nothing, any more. As I said, I was referring to the specific example
you published earlier. When you change the example, you fix the
problem. Let me repeat what I said for those who missed it - I was
not speaking in the general case. Stop putting words in my mouth, er,
keyboard.
So, to review - you posted an example that had a problematic aspect
with respect to threading. You then came back with two different
examples that did not have that problem, and about which I was NOT
speaking, and challenge me to find what's problematic about that. To
which I answer, nothing. So?
Different examples that don't have the problem are different in that
they don't have the problem. Duhhh.
Got it now?
--
Lew