Java 14: Looking at the updated switch statement

JDK 14, released in March 2020, comes with an updated version of the switch statement. This has been a preview feature in JDK 12 and JDK 13.

To see the difference, let's look at a simple example. Assume we want to compute the daily working time based on a DayOfWeek enum.

With the old way of using the switch statement, our solution might look like this:

DayOfWeek day = ...
float expectedWorkingTime;

switch (day) {
	case MONDAY:
	case TUESDAY:
	case WEDNESDAY:
	case THURSDAY:
		expectedWorkingTime = 8f;
		break;
	case FRIDAY:
		expectedWorkingTime = 6f;
		break;
	default:
		expectedWorkingTime = 0f;
}

With the new switch statement (or expression) we can rewrite our example like this:

DayOfWeek day = ...

final float expectedWorkingTime = switch (day) {
	case MONDAY, TUESDAY, WEDNESDAY, THURSDAY -> 8f;
	case FRIDAY -> 6f;
	default -> 0f;
};

So, what's new:

• The switch keyword can be used as expression and return a value. In this example the value returned by switch is assigned to expectedWorkingTime. Note that this allows us to make expectedWorkingTime final which was not possible in the previous solution.
• A case statement can contain multiple values, separated by comma.
• In the case statement, colon is replaced with an arrow (->)
• When using the arrow (->) syntax, no break keyword is required. If you prefer using break, you can still use the older colon syntax for cases.

The new yield statement

In the previous example we return a simple value on the right side of the arrow (->). However, maybe we need to compute this value first, for which we might need a few extra lines of code.

For example:

final float expectedWorkingTime = switch (day) {
	case MONDAY, TUESDAY, WEDNESDAY, THURSDAY -> {
		if (isFullTimeEmployee) {
			yield 8;
		}
		yield 4;
	}
	case FRIDAY -> 6f;
	default -> 0f;
};

Here we use a code block in the first case statement to determine the working time. With the new yield statement we return a value from a case block (like using return in methods).

You can find the examples shown in this post on GitHub.