Switch Expressions in Java (JEP 361)

With Java 14 we will get a new feature that simplifies the switch statement. It will provide a new and clearer way to write switch statements and in addition allows us to use switch as an expression yielding a value.

New Syntax

Forget about break! No fall through anymore – simple and concise.

switch (day) {
    case MONDAY             -> System.out.println("Fully motivated!");
    case TUESDAY, WEDNESDAY -> System.ouFt.println("Get this done!");
    case THURSDAY, FRIDAY   -> System.out.println("Almost done!");
    case SATURDAY, SUNDAY   -> System.out.println("Party time!");
}

Today you would write something like below. Don’t miss the breaks!

switch (day) {
   case MONDAY:
       System.out.println("Fully motivated!");
       break;
   case TUESDAY:
   case WEDNESDAY: 
        System.ouFt.println("Let's get this done!");
        break;
   case THURSDAY:
   case FRIDAY:   
       System.out.println("Almost done!");
       break;
   case SATURDAY:
   case SUNDAY:
       System.out.println("Party time!");
}

Switch Expressions

This is really cool. Now we can asisgn the result of a switch expression to a variable.

String workingDay = switch(day) {
    case 1,2,3,4,5 -> "yes";
    case 6,7 -> "no";
    default -> "don't know";
};

This is easy to read and allows us to simplify our code. Maybe until now you used nested conditional operators (!!) or you introduced a little helper method with return statements.

If you need an actual block to calculate the result of the expression, there is a new keyword you can use for that purpose: yield

String workingDay = switch(day) {
    case 1,2,3,4,5 -> "yes";
    case 6,7 -> "no";
    default -> {
       String defaultAnswer = calculateDefaultAnswer();
       yield defaultAnswer;
    }
};

You can also use the legacy switch syntax and form expressions using the yield keyword.

int result = switch (s) {
    case "Foo": 
        yield 1;
    case "Bar":
        yield 2;
    default:
        System.out.println("Neither Foo nor Bar, hmmm...");
        yield 0;
};

It’s an expression baby

Yes, you can drive your co worker crazy by building complex and inlined switch expressions. It works – I tried it.

public static boolean isWorkingDay(String day) {        
    if ("yes".equals(switch (day) { case "Monday", "Tuesday", "Wednesday", "Thursday", "Friday" -> "yes"; case "Saturday", "Sunday" -> "no"; default -> "dont' know";})) {
        return true;
    } else {
        return false;
    }
}

Try it out today

You can download early access builds from https://jdk.java.net/14/ (just unzip it somewhere you find it again). With Java 14 this is not a preview feature anymore, so you can just start to use the new switch expressions.

Personal opinion

In short: I really like it. I think it makes a lot of sense. Having the privilege to also teach classes in programming I can say that the intention of the programmer when using the switch statement was always a different one – always.

In addition using switch as an expression provides new ways also for a seasoned programmer to simplify their code. Have you ever seen those nested tenary conditional operators?

One downside I see is developers thinking that it is cool to inline switch expressions and combine them to more complex expressions that no one will ever touch again.