Kotlin Programming: The Big Nerd Ranch Guide, First Edition

Nullability

Some elements in Kotlin can be assigned a value of null, and some cannot. We say that the former are nullable and the latter are non-nullable. For example, while you might want a variable in NyetHack that tracks a player’s steed to be nullable, since not every player will ride a steed, you would not want the health points variable to be null. Every player has to have an associated health points value; it would be illogical for them not to. Its value might be 0, but 0 is not the same as null – null is the absence of any value.

Open NyetHack and create a new file called Tavern.kt. Add a main function, where your code will begin executing.

Before opening the tavern to custom drink requests from users, first try an experiment. ...