53. Using yield in switch expressions

Here, we’re going to look at how switch expressions have evolved in JDK 13+.

Java SE 13 added the new yield statement, which can be used instead of the break statement in switch expressions.

We know that a JDK 12+ switch expression can be written as follows (playerType is a Java enum):

return switch (playerType) {
  case TENNIS ->
    new TennisPlayer();
  case FOOTBALL ->
    new FootballPlayer();
  ...
};

Moreover, we know that a label’s arrow can point to a curly-braces block as well (this works only in JDK 12, not in JDK 13+):

return switch (playerType) {
  case TENNIS -> {
    System.out.println("Creating a TennisPlayer ...");
    break new TennisPlayer();
  }
  case FOOTBALL -> {
    System.out.println("Creating a FootballPlayer ...");
    break new FootballPlayer();
  }
  ...
};

Since break can be confusing because it can be used in old-school switch statements and in the new switch expressions, JDK 13 added the yield statement to be used instead of break. The yield statement takes one argument representing the value produced by the current case. The previous examples can be written from JDK 13+ as follows:

return switch (playerType) {
  case TENNIS:
    yield new TennisPlayer();
  case FOOTBALL:
    yield new FootballPlayer();
  ...
};
return switch (playerType) {
  case TENNIS -> {
    System.out.println("Creating a TennisPlayer ...");
    yield new TennisPlayer();
  }
  case FOOTBALL -> {
    System.out.println("Creating a FootballPlayer ...");
    yield new FootballPlayer();
  }
  ...
};

In other words, starting with JDK 13+, a switch expression can rely on yield but not on break, and a switch statement can rely on break but not on yield.