Question

How do I write the getDB() function and use it properly?

Here is a code snippet of my App Object:

public class MyApp extends UiApplication {      private static PersistentObject m_oStore;     private static MyBigObjectOfStorage m_oDB;      static {         store = PersistentStore.getPersistentObject(0xa1a569278238dad2L);     }      public static void main(String[] args) {         MyApp theApp = new MyApp();         theApp.enterEventDispatcher();     }     public MyApp() {         pushScreen(new MyMainScreen());     }      // Is this correct?  Will it return a copy of m_oDB or a reference of m_oDB?     public MyBigObjectOfStorage getDB() {         return m_oDB;  // returns a reference     }  } 

Answer 1

public MyBigObjectOfStorage getDB() {   return m_oDB; } 

As you put it is correct. It will return a copy of the reference, which is kind of in between a copy and a reference.

The actual object instance returned by getDB() is the same object referenced by m_oDB. However, you can’t change the reference returned by getDB() to point at a different object and have it actually cause the local private m_oDB to point at the new object. m_oDB will still point at the object it was already.

See http://www.javaworld.com/javaworld/javaqa/2000-05/03-qa-0526-pass.html for more detail.

Although looking through your code there, you never set m_oDB at all, so getDB() will always return null.