Memory allocation and release

Question

Hi,
i'm having some doubts on the memory issues, like allocation, release, EEPROM and RAM:
Question 1:
private method1()
byte[]a = new byte[10];
byte[]b = JCSystem.makeTransientByteArray(...);
byte c;
When will some memory be allocated to variables a, b and c, and when will that memory be released?
Question 2:
JCRE (until 2.2 at least) doesn't have Garbage collector, but if the card itself has that mechanism, will the applet automatically use it?
Thanks in advance!

Answer 1

It's not a question on how many EEPROM writes are done each day/hout/minute/second. It's a question of whether the data must be saved across sessions. RAM is mainly used for intermediate computations & session data. EEPROM is used to store persistent info (user info, credit, phonebook, etc...).
RAM is also a good way to optimize processing time. If you have to manipulate a lot of persistent data during an APDU, it's a good idea to copy everything in a "cache" (transient buffer) and/or local variables, do all of your processing on the cached values, and then perform the persistent write at the end of the command.
As to your last question on how much RAM is acceptable, it depends on the context. If you know that your applet will be alone, feel free to use as much as the platform can give you. If not, try to be reasonable. Cryptographic intensive applets generally use a lot of RAM to store intermediate computation results.
From personal experience, I've written very simple applets that needed about 20 transient bytes, and complex ones that needed up to 1500 transient bytes. If you really need to set a limit, 200 bytes is already a considerable amount of transient space and should be more than enough for most applets. But then again, my guess is as good as any.