Re: Scope of static class variables

"Red Orchid" <>
Tue, 3 Apr 2007 17:48:43 +0000 (GMT)
I have read your articles in this thread.

Tom Hawtin <> wrote or quoted in
Message-ID <4612603d$0$8725$>:

However, static variables are really evil and should be avoided.

Tom Hawtin <> wrote or quoted in
Message-ID <46126833$0$8732$>:

Christoph wrote:

Not to question good programming style, but are there any cases were
non-final static variables are "okay" to use (for example in this
case, where they remain the same as long as the program runs, but
aren't hard-coded)?

It's very rare. There are some examples where you have a private static
final, to an object that is mutated.

The common example of "final static" variable is the instance of
a thread-safe class. For example,

class XYZ {
    private static final Pattern pat = Pattern.compile("....");

    boolean findXX(String s) {
        Matcher m = pat.matcher(s);

"Pattern" is thread-safe and only one "pat" is enough/good for all
the instances of "XYZ".

What is your comment?

I think that it is not rare that static variables are not evil.
For example, (These are common cases.)

Case 1) : Thread-Safe
     Write a class that returns the unique string for the entire scope of App.
     (Maybe, "Message-ID" is the typical example that uses this class).

Case 2) : Thread-Safe
     Write a class that calculates the network traffic for the entire scope of App.

I think that static variables should be used. That is,

<Imp of Case 1>
final class UniqueString {
    private static long _val = ...;

    private UniqueString() {
        // no-op
    public synchronized static String nextVal() {
        return "....." + (_val++);
</Imp of Case 1>

If _val is not "static", it is possible that unique string is not guaranteed.
Because multiple instances of "UniqueString" is not prohibited.
Singleton is not proper for this case because "static" is simple.

<Imp of Case 2>
// Analogous to Implementation of Requirement 1
</Imp of Case 2>

How do you implement the above cases ?

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