Pattern matching for instanceof

Definition

Pattern matching for instanceof (Java 16) checks a type and gives you a typed variable in one step. You no longer need a separate cast after the check.

Example code

No cast after instanceof

class Demo {
    static String describe(Object value) {
        if (value instanceof String s && s.length() > 3) {      // s is a String right here
            return "long text: " + s.toUpperCase();
        } else if (value instanceof Integer i) {
            return "number plus one: " + (i + 1);
        }
        return "something else";
    }

    public static void main(String[] args) {
        System.out.println(describe("hello"));
        System.out.println(describe(41));
        System.out.println(describe("hi"));
    }
}

// Output:
// long text: HELLO
// number plus one: 42
// something else