Re: this reference in Java constructors

Lew <>
Thu, 29 Oct 2009 10:37:51 -0700 (PDT)
On Oct 29, 1:26 pm, Eric Sosman <> 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() {
        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() {

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=


is no further state to observe. Apples and oranges.

     System.out isn't static? PrintStream has no observable stat=


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=


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,

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?


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