Re: Static Variables and JAR Files
Jason Cavett wrote:
class Base {
protected static String someInfo = null;
public Base() {
// instantiate
}
}
class Child extends Base {
public Child() {
if(Base.someInfo == null) {
someInfo = new String("String Here");
}
}
}
This code runs an inherent risk of multiple instantiation of the 'someInfo'
variable, in a multi-threaded context.
I have a couple other children that also extend base and, if someInfo
is null, they give the String their own value.
So what is 'someInfo' supposed to be when multiple children instantiate? It's
a suspect pattern to have different children instantiate a parent-class static
member with different values. Part of the problem is that it creates a
dependency between not only the parent to the child class, but between child
classes. Now they have to be aware of the semantics of specific String (not
enum?!) values in a shared variable.
Another problem is that class loading in a different order can cause
non-deterministic behavior - on some runs the 'someInfo' will settle
eventually to one value, on other runs to a different value.
If multiple threads grab the class, even via the same class loader, each
thread could instantiate the variable to a different value and use that value
locally throughout its run. The value change might not be visible to the
other or any subsequent thread.
It is likely that removing this static variable will be a better solution than
trying to get all that right.
--
Lew