Custom MDP with RL4J

How do I implement a custom MDP with RL4J?

We simply need to implement the MDP interface. We can use existing ones as templates:
https://github.com/eclipse/deeplearning4j/blob/master/rl4j/rl4j-ale/src/main/java/org/deeplearning4j/rl4j/mdp/ale/ALEMDP.java
https://github.com/eclipse/deeplearning4j/blob/master/rl4j/rl4j-gym/src/main/java/org/deeplearning4j/rl4j/mdp/gym/GymEnv.java
etc.