Get Constant data from firebase in Android

How to get a constant value from firebase?

I'm maintaining a global count variable of number of friends a user has. Everytime user wants to add friends I need to increment that variable. How can I achieve this.

If I use a OnDataChangeListener() I will be able to read the DataSnapShot only when there is some change in data. But I want to read the data even when some part of the data has not changed.