Switch Expressions in Java

Modern Java switch can be used as an expression: it evaluates to a value. It also provides arrow labels that avoid accidental fall-through.

Switch expressions became a standard feature in Java 14.

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Traditional switch

Traditional switch statements usually need break to prevent one case from continuing into the next.

String dayType;

switch (day) {
    case SATURDAY:
    case SUNDAY:
        dayType = "Weekend";
        break;
    default:
        dayType = "Weekday";
}

This works, but assigning a result in every branch can become repetitive.

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Arrow-Style Switch Expression

Use -> and assign the result directly.

String dayType = switch (day) {
    case SATURDAY, SUNDAY -> "Weekend";
    default -> "Weekday";
};

System.out.println(dayType);

The semicolon after the closing brace ends the assignment. Arrow cases do not fall through, so no break is needed.

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Multiple Labels

Put labels separated by commas when they share the same result.

int daysInMonth = switch (month) {
    case APRIL, JUNE, SEPTEMBER, NOVEMBER -> 30;
    case FEBRUARY -> 28;
    default -> 31;
};

For real calendar code, use YearMonth.lengthOfMonth() because February can have 29 days.

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Blocks and yield

When a case needs more than one statement, use a block and return the expression’s value with yield.

String shippingMessage = switch (status) {
    case "PAID" -> "Preparing your order";
    case "SHIPPED" -> {
        String trackingUrl = "https://example.com/track";
        yield "Track your package: " + trackingUrl;
    }
    case "DELIVERED" -> "Order delivered";
    default -> "Unknown order status";
};

yield is specific to a switch expression. It returns a value from that case block.

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Exhaustive Cases

A switch expression must produce a result for every possible input. For enums, list every constant or include default.

enum TrafficLight { RED, YELLOW, GREEN }

String action = switch (light) {
    case RED -> "Stop";
    case YELLOW -> "Slow down";
    case GREEN -> "Go";
};

No default is required because all enum constants are covered. If a new constant is added later, the compiler will point out the switch expressions that need updating.

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Statement or Expression?

Use a switch statement when each case performs actions. Use a switch expression when the purpose is to calculate one value.

switch (command) {
    case "start" -> service.start();
    case "stop" -> service.stop();
    default -> System.out.println("Unknown command");
}

Prefer the arrow form for new code unless you specifically need the older fall-through behaviour.

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Next Steps ➡️

Combine switch expressions with Sealed Classes when your application models a known set of types.