Java: What is pattern matching for switch in Java 21?

1public static String format(Object obj) {
2    return switch (obj) {
3        case Integer i -> "Integer: " + i;
4        case String s when s.length() > 5 -> "Long string: " + s;
5        case String s -> "String: " + s;
6        case null -> "null";
7        default -> "Unknown: " + obj;
8    };
9}
10
11// Pattern matching with sealed classes
12sealed interface Shape {}
13record Circle(double radius) implements Shape {}
14record Rectangle(double w, double h) implements Shape {}
15
16double area(Shape shape) {
17    return switch (shape) {
18        case Circle c -> Math.PI * c.radius() * c.radius();
19        case Rectangle r -> r.w() * r.h();
20        // No default needed — sealed class has exhaustive types
21    };
22}
23
24// Nested pattern matching
25record Wrapper(Object value) {}
26
27string describe(Wrapper w) {
28    return switch (w) {
29        case Wrapper(Integer i) -> "Integer wrapper: " + i;
30        case Wrapper(String s) -> "String wrapper: " + s;
31        case Wrapper(null)      -> "Empty wrapper";
32        case Wrapper(var v)      -> "Other wrapper: " + v;
33    };
34}