Are all .class files in my Java application loaded into memory after application start?

Question

I am making an app for Android, in my Activity I need to load an array of about 10000 strings. Loading it from database was slow, so I decided to put it directly into one .java file (as a private field). I have about 20 of these classes containing string arrays and my question is, are all the classes loaded into memory after my application is started? If so the Activity in which I need these strings would be loaded quickly, but the application as a whole would have a slow start... Is there other way, how to very quickly load an 10000 string array from a file?

UPDATE: Why I need these strings? My Android app allows you to find "journeys" in Prague's public transit - you choose departure stop, arrival stop and it finds your journey (have a look here). My app has a suggestions feature - you enter leter "c" as your departure stop and a suggestions ListView appears with stops starting with "c". For these suggestions I need the strings. Fetching the suggestions from database is slow (about 400ms on G1).

Answer 1

First, 400ms to perform a simple database query is really slow. So slow that I'd suspect that there is some problem in your database schema (e.g. indices) or your database connection configuration.

But if you a serious about not using a database, there are a couple of alternatives to what you are currently doing:

1. Arrange that the classes containing the arrays are lazily loaded as required, using Class.forName(...). If you implement it right, it should be possible for the garbage collector to reclaim the classes after they have been loaded and the strings have been added to your primary data structure.

2. Turn the 10000 Strings into a flat file, put the file into your app's JAR file. Then use Class.getResourceAsStream(...) to open the file and read it into the in-memory array.

3. As above, but using an indexed file and replacing the array with a data structure that allows you to read Strings from the file lazily. (This will be a bit complicated, but if you are worried by the memory consumed by the 10000 Strings, this will help address that.)