For the sake of safety all of Android processes(apps) are running inside of what's called "sandbox". Which means that unlike a Windows application, which upon being executed "sees" all of your computer (can access your harddrive, read/create files, access network, access peripherals) the Android app doesn't have direct access to phones/tablets "drive" (internal permananent storage). Neither it sees any other processes running to be able to send them anythnig. And neither your apps process is visible to any other app on the system, thus making it impossible to exchange data (or for vi_ru_ses to in_fect other apps).
Every app has it's own folder, where it stores it's files. But:
a) apps are not allowed to write arbitrary data to that folder
b) apps can only write into that folder under one condition: if what they write is sqlite3 database and they use Android sqlite API
c) still none of other apps is able to read this sqlite database, as it's in applications folder
But still some processes need to provide data to share with other processes (an example is system app which stores and provides access to your address book: it runs on you phone as service constantly on the background and provides your address book details to different apps : like phone book or your custom text messaging or skype or viber or whatver).
This is done through mechanism called "Content Provider". There're few good tutorials about Content Providers available,
but keep in mind that writing it in PDE would be probably immensely hard and error prone (if not impossible) and you will need to use Eclipse.
Maybe you will want to split your sketch into two parts:
one will be just "Content Provider app" which will be only managing data and will be written in Eclipse, wherease your sketch would be written in PDE and wouldn't store data, but just consume/update
If all of that sounds a bit too complicated, maybe the simplier solution would be to store your database on SD card. Files on SDCard are available for reading/writing for all apps. (Provided you have given app WRITE_EXTERNAL_STORAGE permission). However I am not sure how good SQLite would be in case you are going to be updating the same sqlite file from different processes. You will have to come up with some "synchronization" method.
Also keep in mind that when writing to SDCards, because of their architecture, writing to the card may "freeze" for good few seconds when SD card is sometimes "rearranging electrons" to fit your newly written data. Thus writing to SD card cannot happen on your drawing thread ( originating from
draw() )
