Re: Initializing Singletons
Jason Cavett wrote:
I'm curious - is it possible (and if so, how) to initialize a
Singleton class when the class used for initialization must also get
an instance of the Singleton class?
Here's a pseudocode example to make that more clear...
class SingletonClass {
private SingletonClass() {
ConfigFileReader reader = new ConfigFileReader();
reader.read();
}
// other singleton stuff
}
class ConfigFileReader {
public ConfigFileReader() {
// do stuff
}
public void read() {
// read in the config file and get the appropriate information
SingletonClass.getInstance().setValues(...);
}
}
I don't *think* what I want to do is possible. But, if it is, I'm not
sure how to do it. Any insight would be appreciated.
Thanks
Without seeing getInstance, I can't be certain, but it looks like you'll
get infinite recursion... It would be better to use dependency injection
instead... If you absolutely *need* to use singleton (one of the most
abused patterns, BTW), you can try this:
public static SingletonClass getInstance() {
if (instance == null) {
instance = new SingletonClass();
ConfigFileReader config = new ConfigFileReader(instance);
config.read();
}
return instance;
}
SingletonClass() now should do nothing, or at least only construction
related activities.
getInstance() will never return an uninitialized instance.
ConfigFileReader gets an explicit instance to read into. Much more
flexible for unit testing, etc...
In an ideal application, for every class that needed access to
SingletonClass, you would have a setSingletonInstance(...) method, and
use an injection container such as Guice or Spring (to name only two).
Hope this all helps.
Daniel.
--
Daniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/>