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

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.)

A class is loaded only when it is first referenced.

Though you need an array of 10000, you may not need all at once. Here is where the concept of paging comes in. This link indicates that Paging is often done in Android.Initialy have only a small amount of array in memory, and as you need it, keep loading it in to memory and unloading any previous data from memory if not wanted.

For e.g. in any table, at one shot, the user may see at best 50 records, then he will have to scroll(considering his screen is not size of an iMax movie theatre). When he scrolls, load the next chunk of data and unload any data that is now inivsible to the user.