No Static Method in Interface, So I Write Code As ...

Java does not support static method in interface. But sometimes, I just want a static method to say: PersistenceManager.getDefault(), where PersistenceManager is going to be an interface. I don't like to add one more class named PersistenceManagerFactory, with a method:

public static PersistenceManager PersistenceManagerFactory.getDefault()

So I write code like:

public class PersistenceManager {
    private static I i;

    public static I getDefault() {
        return i == null ? i = ServiceLoader.load(I.class).iterator().next() : i;
    }
    
    /** The interface I, which is actually the PersistenceManager should be: */
    public static interface I {
        
        void saveQuotes(String symbol, Frequency freq, List<quote> quotes);
        List<quote> restoreQuotes(String symbol, Frequency freq);
        void deleteQuotes(String symbol, Frequency freq, long fromTime);
        void dropAllQuoteTables(String symbol);
        
        void shutdown();
        
        QuotePool getQuotePool();
        TickerPool getTickerPool();
    }
    
}

Then implement the PersistenceManager.I in another package, like:

public class NetBeansPersistenceManager implements PersistenceManager.I {
   ...
}

And declare it under the META-INF as:

core/src/META-INF/services/org.aiotrade.math.PersistenceManager$I

which contains one line:

org.aiotrade.platform.core.netbeans.NetBeansPersistenceManager

I can call PersistenceManager.getDefault().showdown() now.