other midlets interaction in suit + class loading of midlets

[TacB0sS]

Hey guys,
I'm wondering when I start my midlet one out of 10 in the suit, does all the suit loads into the memory, or only the midlet classes as it uses them?

I know classes loading process is different between devices, but loading midlets? is there some behavior I can count on?

[grahamhughes]

Behaviour you count on... hmmmm... that's always tricky. There's nothing strict in any specification about when a MIDlet class must be loaded. And even if it's in the specification, counting on it isn't always possible!

As a general... I hestitate to say "rule"... let's say "observation"... MIDlet loading is implemented something like:

String midletClassName = readMidletClassNameFromJad(index);
MIDlet midlet = (MIDlet) (Class.forName(midletClassName).newInstance());
midlet.startApp();

We can tell that Class.forName() is used, because if the MIDlet class is missing, we see a ClassNotFoundException (thrown by the runtime library), rather than a NoClassDefFoundError (thrown by the VM).

I'm not aware of any implementation loading all the MIDlets. I guess it's possible than an implementation might load the all before the menu of them is displayed, in order to verify that they all exist, but I have no evidence that this happens.

For me, a bigger worry would be what happens when the MIDlet terminates, and you return to the list of MIDlets in the suite (for devices that display a two-level menu, one of suites, then a second level of MIDlets in the suite). Does the VM terminate at the point? If it doesn't, then all the classes are still loaded, and their static variables will retain their state.

Personally, I'd avoid multiple MIDlets in a suite, mainly because I just don't have enough experience of how different devices behave.

Graham.

[TacB0sS]

Thanks, Graham,

here is the deal,
I would like to use one midlet to be the main application, and another to be for example a sort of a connector to data, if it need to read from RMS, files, internet, what ever unknown operation to retrieve data, and since my main application is big enough and if I have resources that would only work once in a while, I would like to use them and dispose of them, and since class loading is an issue I was wondering, does each midlet has its own class loader? could I transfer information between them? I know I should learn more about multiple midlets, I just want to know if it worth investigating...

there are other operations I use once in a while, or some even once, that I would not like to load into the memory every time the application starts

[grahamhughes]

There will be only one class loader. In CLDC implementations, the class loader is part of the VM, and not an instantiable component. Whether or not classes are disposed of depends on whether or not the VM terminates in between. There's no guarantee.

Communicating between MIDlets in a suite is possible by RMS - RMS is per suite, not per MIDlet, so all MIDlets in the same suite share the same record stores. There is no signing or permission involved.

[TacB0sS]

how about storing data on a static var on one midlet and read it from another, not very OO, but would it do?
Adam.

[grahamhughes]

No, since there's no guarantee that the VM would remain active after terminating one MIDlet, and before launching the other.