Re: Initializing Singletons

Daniel Pitts <>
Thu, 08 May 2008 18:10:33 -0700
Jason Cavett wrote:

On May 8, 11:02 am, Daniel Pitts
<> wrote:

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();;
  // other singleton stuff
class ConfigFileReader {
  public ConfigFileReader() {
    // do stuff
  public void read() {
    // read in the config file and get the appropriate information
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.

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);;
    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 Pitts' Tech Blog: <>

"If you absolutely *need* to use singleton (one of the most abused
patterns, BTW)"

I have my own opinions on this, but I'm curious - when *should* you
use a singleton pattern (in your opinion)? I'm not trying to start a
flame war, but, being a software engineer, I like seeing other
people's viewpoints on the matter.

Either way, I did get it to work. Thanks for the help.

Actually, the pattern that is abused is the "static" singleton. The
framework for your application should instantiate one instance and pass
it where it needs to go. This is appropriate for a lot of objects that
should be accessible "system wide". Dependency Injection is exclusive
with regards to Singletons, and I think a lot of people would be happier
if they mixed to two appropriately :-)

As far as appropriateness for static singletons, I can't think of any

Daniel Pitts' Tech Blog: <>

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