-snip-
I'm reading the OP's question in a different way. He wants to ensure the private key has been written to disk so that if there is sudden power loss you don't loose bitcoins. Sort of an atomic operation. I don't think he's worried about some malware reading the keys from memory. If you have malware it could just as easily read the keys from disk.
(Also, electrum is coded in python not java. Your point about lack of low level hardware access stands, though.)
You are probably right, now that I read it again "write behind cache" makes more sense if we are talking about writing to HDD.
But wouldnt this only be relevant after creating a new private key? So If I want to be paranoid about that a reboot would indeed be a solution. Open wallet -> create new private key and address -> close wallet -> reboot system -> open wallet and use the newly generated address. Repeat if you need a new address or generate a sufficient number of addresses the first time.
I suspect he's been reading this thread:
https://bitcointalksearch.org/topic/lost-44-btc-678910Well my interpretation of the lack of response form OP in that thread is that OP actually found the private key in said folder but is ashamed to admin that the solution was that obvious
Either that or losing this many coins drove him/her away from bitcoin forever.
in June i created another receiving address
Yet posted it in July. I would be very surprised if MultiBit would not write the private key to disk after days (at least 6 if the time OP posted is any indictator).
Anyway. I just realized a way to make sure you have all the private keys on (at least one) disk. Make a backup on a USB drive after creating a new address. This way when you (properly) remove the drive from the machine you know that the OS commited the write to (at least) the USB drive. In case anything goes wrong you can restore from that backup.
This is probably the only 100% way anyway, since writing to disk is ultimatly a system call which could be faulty. A backup on USB (or any other removeable media) would allow you to verifiy the backup with another machine, preferably running a different OS. I think we are back in the tin foil hat area again
Id recomment regular, redudant backups anyway, depending which wallet you use. The data on your disk could be corrupted any time so after creating new private key(s) a new backup should be common sense.
This is void if you use a wallet like electrum or dark wallet where you only need to backup the initial seed once.
Bitcoin core has several private keys allready pregenerated thus - in theory - you only have to backup every 100 new addresses.