54. Tackling the case null clause in switch

Before JDK 17, a null case in a switch was commonly coded as a guarding condition outside the switch, as in the following example:

private static Player createPlayer(PlayerTypes playerType) {
  // handling null values in a condition outside switch
  if (playerType == null) {
    throw new IllegalArgumentException(
     "Player type cannot be null");
  }
  return switch (playerType) {
    case TENNIS -> new TennisPlayer();
    case FOOTBALL -> new FootballPlayer();
    ...
  };
}

Starting with JDK 17+ (JEP 427), we can treat a null case as any other common case. For instance, here we have a null case that is responsible for handling the scenarios when the passed argument is null:

private static Player createPlayer(PlayerTypes playerType) {
  return switch (playerType) {
    case TENNIS -> new TennisPlayer();
    case FOOTBALL -> new FootballPlayer();
    case SNOOKER -> new SnookerPlayer();
    case null -> throw new NullPointerException(
                   "Player type cannot be null");
    case UNKNOWN -> throw new UnknownPlayerException(
                      "Player type is unknown");
    // default is not mandatory
    default -> throw new IllegalArgumentException(
                 "Invalid player type: " + playerType);
  };
}

In certain contexts, null and default have the same meaning, so we can chain them in the same case statement:

private static Player createPlayer(PlayerTypes playerType) {
  return switch (playerType) {
    case TENNIS -> new TennisPlayer();
    case FOOTBALL -> new FootballPlayer();
    ...
    case null, default ->
      throw new IllegalArgumentException(
       "Invalid player type: " + playerType);
  };
}

Or you might find it more readable like this:

...    
case TENNIS: yield new TennisPlayer();
case FOOTBALL: yield new FootballPlayer();
...
case null, default:
  throw new IllegalArgumentException(
    "Invalid player type: " + playerType);
...

Personally, I suggest you think twice before patching your switch expressions with case null, especially if you plan to do it only for silently sweeping these values. Overall, your code may become brittle and exposed to unexpected behaviors/results that ignore the presence of null values. In the bundled code, you can test the complete examples.