Basics

5. Switch Expressions

Switch expressions (Java 14+) replace the error-prone fall-through statement form with arrow labels, a yield keyword, and the ability to return a value — eliminating most break bugs.

Java 14+ (standard)

Explanation

Classic switch statements have fall-through semantics (a missing break silently continues into the next case) and cannot return a value directly. Switch expressions (JEP 361, standard since Java 14) fix both problems.

Arrow labels (case X -> ...) do not fall through. To return a value from a multi-statement arm, use yield. Switch expressions must be exhaustive — the compiler enforces that all possible values are handled, either with explicit cases or a default.

When combined with sealed classes or enums (Java 17+) and pattern matching (Java 21+), switch expressions become a powerful tool for algebraic data processing with full compiler-enforced exhaustiveness.

Example

public class SwitchExpressions {
    sealed interface Shape permits Circle, Rectangle, Triangle {}
    record Circle(double radius) implements Shape {}
    record Rectangle(double w, double h) implements Shape {}
    record Triangle(double base, double h) implements Shape {}

    static double area(Shape s) {
        // Pattern matching switch — exhaustive over sealed type
        return switch (s) {
            case Circle c    -> Math.PI * c.radius() * c.radius();
            case Rectangle r -> r.w() * r.h();
            case Triangle t  -> 0.5 * t.base() * t.h();
        };
    }

    public static void main(String[] args) {
        // Simple value switch with arrow labels (no fall-through)
        int day = 3;
        String name = switch (day) {
            case 1 -> "Monday";
            case 2 -> "Tuesday";
            case 3 -> "Wednesday";
            case 4 -> "Thursday";
            case 5 -> "Friday";
            default -> "Weekend";
        };
        System.out.println(name); // Wednesday

        // yield for multi-statement arm
        String label = switch (day) {
            case 1, 2, 3, 4, 5 -> {
                String d = name.toLowerCase();
                yield "Weekday: " + d;
            }
            default -> "Weekend";
        };
        System.out.println(label);

        System.out.printf("Circle area: %.2f%n", area(new Circle(5)));
    }
}

Sources