22. Pattern Matching for instanceof

The Scenario

Java 16 introduced pattern matching for instanceof, which simplifies the common "check-then-cast" idiom. This is a significant enhancement to how we handle polymorphism safely.

Predict the output of the following code.

class Shape { }
class Circle extends Shape {
    double radius = 5.0;
    void info() { System.out.println("Circle"); }
}

public class Main {
    public static void main(String[] args) {
        Object obj = new Circle();

        if (obj instanceof Circle c && c.radius > 0) {
            c.info();
            System.out.println(c.radius);
        } else {
            System.out.println("Not a positive circle");
        }
        
        // Scope Check
        // System.out.println(c.radius); // Will this work?
    }
}

Take Your Shot

Predicted Output

Type exactly what you think will be printed in the console.