Question

I am creating a library project for a number of android apps.
The apps all have some common functionality that I wish to include in the library project but the library project functions require use of application specific constants

So I am looking for a way to provide the library functions with the names of the constants and allow each app to define them

An example of a specific app constant and how it is used within the library project

public class AppConstants {
    public static final long APP_ID = 6;//Needs to be set for each app
}

public static long getCurrentAppId(Context context) {
    return getLongPreference(context, CURRENT_APP_ID_KEY, AppConstants.APP_ID);
}

This is just one example of approximately 60 constants that need to be defined for each app for a large number of library functions

Obviously I would normally just import/include the project specific app_constants.java file but this is not possible in the library project files as it hasn’t got a clue about the specific applications (rightly so)

So what is the best way to have each specific app override the constants?

Update
I took a long time deciding on which of the superb answers I have been provided with best suited my needs (Thanks everyone) In the end I chose the xml solution. I don’t particularly like it because it clutters up my apps resources and I did seriously consider using the interface solution but the xml solution does work nicely

Answer 1

Option #1
Extend your AppConstants class in each project

Better Option#2
Use XML resources to define the constants

<?xml version="1.0" encoding="utf-8"?>
<resources>
<item type="integer" name="app_id" format="integer">6</item>
</resources>

then you can retrieve them by

Context.getResources().getInteger(R.integer.app_id);

add the xml file to your resources in each project with only the values you need different