getApplicationContext() on a null object reference

public class Distance extends Application

Do not randomly extend classes, just because you think that it will clear up a compiler error. You do not have a valid Application subclass here, and you are not using it properly.

Step #1: Remove extends Application from Distance.

Step #2: Have getDistance() take a Context as a parameter, and have it use that with MySingleton

Step #3: Have MainActivity pass getApplicationContext() into getDistance() as the Context