If you are trying to connect to the Ethereum network from a native mobile application, check out this Geth tuorial for Android. This is their Github link.
I have also encountered this library, Ethereum Android, but unsure of its capabilities yet.
A third option that I found promising is Web3j.
Although they all look like very promising and there have been development on them for quite some time it is a little weird that there aren't enough tutorials and documentations about them or even implementations on mobile apps that connect to the Ethereum Network.
I am also pursuing the same goal so feel free to contact me further.
Edit: So after further research and referring to Jaime's answer, I was able to use web3j library to create Java objects of my smart contract provided that I had the source code and web3j also connects me to the client which in my case was an Infura client which is a link that you get when you sign up with Infura for free. I was able to use Java objects, which represented the smart contract, and invoking its methods which interacted with the Ethereum main net (or test net if that's what you want).