Oh - almost forgot. Look at the presentation from Google I/O 2009 on programming for performance and gaming (I forget the title). It was really good, because the presenter gives some other really good general performance tips.
Cheers, Richard Schilling Root Wireless On Jul 22, 1:17 pm, Richard Schilling <[email protected]> wrote: > Yes, there were some good suggestions. And, yes, using the database > is a great idea. But I have another, and I use this general approach > a lot when I need to import/export data or just ship files around on a > device, or when memory and performance are key. > > XML parsers, streaming or in-memory DOM are time consuming and often > not ncessary when you're working with simple data like strings. XML > is best used when you need to tag the data with a lot of attributes. > Not only that, but XML bloats the memory requirements of your > application multiple times because you have to save all XML characters > (e.g. '<', '='). > > You'll get the most speed out of processing, especially I/O operations > if you first reduce each note to a binary form (e.g. array of > characters). If you need to store all the notes in a single file, > then I would suggest some format like this: > > HEADER LENGTH STRING HEADER LENGTH STRING .... .etc ..... > > Here's some code. > > public static byte[] encode(String s){ > > byte[] header = "CAFEBABE".getBytes(); // or some other magic > token > byte[] chars = s.getBytes(); > byte[] sizeBytes = intToByteArray(chars.length); // convert > an int > to a byte array - defined elsewhere. > > int totalLength = header.length + chars.length + > sizeBytes.length; > ByteBuffer buf = ByteBuffer.allocate(totalLength); > buf.put(header); > buf.put(sizeBytes); > buf.put(chars); > > buf.position(0); > return buf.array(); > } > > Pass each string in, and then pack the results from each call into > your file. > > Richard Schilling > Root Wireless > > On Jul 22, 12:57 pm, gnugu <[email protected]> wrote: > > > > Just creating 1000 objects isn't going to take 45 seconds, it sounds like > > > I was running it in the emulator with the debugger attached. I'll > > check logs and try the profiler. > > > Thanks. > > > On Jul 22, 12:02 pm, Dianne Hackborn <[email protected]> wrote: > > > > Just creating 1000 objects isn't going to take 45 seconds, it sounds like > > > you have something really bad going on somewhere. With it taking that > > > amount of time, you will probably quickly see some serious hot spots if > > > you > > > run the profiler. > > > > Also if you are seeing log messages about the GC running during that time, > > > this means that something in your code is creating tons and tons of > > > temporary objects. Again the profiler should help a lot in tracking this > > > down. > > > > On Wed, Jul 22, 2009 at 11:39 AM, gnugu <[email protected]> wrote: > > > > > Dianne, > > > > > It is not reading and writing that's slow. > > > > > I have a class that has Notes field (ArrayList<Note>). I wrote my test > > > > to create 1000 note objects and add it took 45 seconds. > > > > Because I can't get XML string out of DOM Document I can't use the > > > > Document as my storage for notes which leaves me with creating all > > > > these objects as I read the XML. > > > > > It would be ideal for me to use MySQL to store the notes but then I > > > > would want to encrypt the table as a whole rather then individual > > > > records. > > > > > My own binary format might work if I create my own data reader that > > > > would work on my binary data. That's a lot of work. > > > > > Hmm, I wonder if I could simply encrypt the database file. But then > > > > how do I feed it to DatabaseHelper? > > > > > On Jul 22, 11:26 am, Dianne Hackborn <[email protected]> wrote: > > > > > Which part is slow, reading or writing? If it is writing, just stay > > > > > the > > > > > heck away from the standard XML writers, they are horrendous. There > > > > > is a > > > > > FastXmlSerializer with limited functionality that you could copy out > > > > > of > > > > the > > > > > source code for your own use: > > > > > >http://android.git.kernel.org/?p=platform/frameworks/base.git;a=blob;... > > > > > > That said, XML is just pretty intrinsically inefficient to read and > > > > write. > > > > > I have been yelled at more than once about using it at all. :) If the > > > > > amount of data you are storing is relatively large, you may want to > > > > > just > > > > use > > > > > your own binary format. Yes, this does require a lot more work to > > > > > deal > > > > with > > > > > compatibility as the format changes and such, but often that is worth > > > > > it, > > > > > > On Wed, Jul 22, 2009 at 9:23 AM, gnugu <[email protected]> wrote: > > > > > > > Hi, > > > > > > I'm working on an application where I want to save bunch of > > > > > > information in the XML file. I am not using MySQL because I want all > > > > > > the info to be encrypted and in one place. I don't know how this > > > > > > could > > > > > > be done in the data base. > > > > > > > I was thinking that I would use DOM Document for my data adapter to > > > > > > bind with ListView. But I found out that there is no way of getting > > > > > > the XML out of DOM Document to save it to the file! > > > > > > > So now I use SAX to read XML and create bunch of objects one for > > > > > > each > > > > > > piece of data in memory. > > > > > > > The SDK Guide in Designing for Performance says to avoid creating > > > > > > objects (http://developer.android.com/guide/practices/design/ > > > > > > performance.html#object_creation< > > > >http://developer.android.com/guide/practices/design/%0Aperformance.ht...> > > > > > > ). > > > > > > > I understand and agree and even proved that the performance sucks > > > > > > if I > > > > > > do it the way I described above. > > > > > > > What other choice there might be? Anybody has any suggestions how I > > > > > > could save bunch of notes and have them all encrypted with ONE > > > > > > password as a key base? I know I could use that one key to encrypt > > > > > > every database row, but then changing the password would be > > > > > > difficult. > > > > > > > Any suggestions? > > > > > > > Thanks. > > > > > > -- > > > > > Dianne Hackborn > > > > > Android framework engineer > > > > > [email protected] > > > > > > Note: please don't send private questions to me, as I don't have time > > > > > to > > > > > provide private support, and so won't reply to such e-mails. All such > > > > > questions should be posted on public forums, where I and others can > > > > > see > > > > and > > > > > answer them. > > > > -- > > > Dianne Hackborn > > > Android framework engineer > > > [email protected] > > > > Note: please don't send private questions to me, as I don't have time to > > > provide private support, and so won't reply to such e-mails. 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