Static instance variable references instance of the class

Question

Can I let a static field of a class keep a reference to an instance of itself? If so, will it keep alive in the jvm without anyone else keeping a reference?

public class StatTest {
    private static StatTest statTest;

    public static StatTest getStatTest () {
        if (statTest== null) {
            statTest= new StatTest ();
            statTest.init();
        }
        return statTest;
    }

    private StatTest() { }
}

This is one way to implement the singleton pattern. Just note that this is not thread-safe (ie, things might get broken if you call StatTest.getStatTest() from more than one thread). To compare different singleton implementations (including some thread-safe ones), check stackoverflow.com/questions/7121213/singleton-instantiation/…, an answer I wrote some time ago. — Bruno Reis
– Bruno Reis, Commented Nov 9, 2011 at 9:21
Thank you for all the answers! I realize now that this is a really well known pattern. I recognize the name singleton from before, but I've never read about it. Now it will be easy to find information on how to proceed. Thanks alot! — joaerl
– joaerl, Commented Nov 9, 2011 at 9:38

Abimaran Kugathasan · Accepted Answer · 2011-11-09 09:12:44Z

7

Yes, This is the concept of the Singleton design pattern!

answered Nov 9, 2011 at 9:12

Abimaran Kugathasan

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Kristof Mols · Accepted Answer · 2011-11-09 09:11:59Z

2

This is one way to create a singleton of a class.

So to answer your question:

Yes, it is possible
All references to the getStatTest() method will return that instance.

When using this method for a singleton, the method is mostly called getInstance() =)

answered Nov 9, 2011 at 9:11

Kristof Mols

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Michael Borgwardt · Accepted Answer · 2011-11-09 09:14:56Z

1

will it keep alive in the jvm without anyone else keeping a reference?

Yes, as long as the class itself is not eligible for garbage collection (which can only happen if you use a custom classloader).

answered Nov 9, 2011 at 9:14

Michael Borgwardt

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bpgergo · Accepted Answer · 2011-11-09 09:12:39Z

0

Congrats. You've reinvented the singleton. http://en.wikipedia.org/wiki/Singleton_pattern

answered Nov 9, 2011 at 9:12

bpgergo

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