Re: can I have a static variable in multilethread environment?

From:

Patricia Shanahan <pats@acm.org>

Newsgroups:

comp.lang.java.programmer

Date:

Fri, 05 Oct 2007 11:12:28 -0700

Message-ID:

<fe5uqd$1bmf$1@ihnp4.ucsd.edu>

www wrote:

Hi,

I *really* hope to have a static variable in Class A. It is a
PrintWriter. All other classes, Class B, Class C, etc, need that
variable to print out logging message.

If not static, it is really hard to pass that variable around, one class
calling another, which calls another class. If it is static, e.g:

public Class A {
public static PrintWriter _logger = new PrintWriter(new
FileOutputStream("mylog.txt"));
...

}

Then in other classes, if need to log some message, just:

A._logger.println("Here is the new message");

However, my program will be run in multilethread environment. The above
approach is not acceptable.

Is there a way to get around?

Thank you very much.

Do all threads need the same value, or different values, and does the
value change?

If the same, non-changing value, I think a simple static variable is the
answer. The initialization is protected by the rules for class
initialization. See
http://java.sun.com/docs/books/jls/third_edition/html/execution.html#12.4.2

If it changes, you need synchronization to manage the changes.

If different threads need different values, use ThreadLocal.

Patricia