Challenge 2: Dynamic Dispatch Through a Shape-Typed Variable — Possible Solution
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DispatchDemo.java:

public class DispatchDemo {
    public static void main(String[] args) {
        Shape s = new Circle(2.0);
        System.out.println(s.area());

        // Even though `s` is DECLARED as type Shape, calling s.area()
        // runs Circle's overridden version, not Shape's own
        // 0.0-returning version. This is dynamic dispatch: Java looks
        // at the object's ACTUAL runtime type (Circle) to decide which
        // area() to run, not the variable's declared compile-time type
        // (Shape).
        //
        // This happens automatically because every Java instance
        // method is virtual by default -- no keyword needed to opt in.
        // In C++ (cpp1-7), this same behavior would require area() to
        // have been explicitly marked `virtual` in the base class;
        // without that keyword, C++ would statically bind to Shape's
        // own area() based on the declared type alone, ignoring the
        // real object underneath.
    }
}

Output:

    12.566370614359172

WHY THIS WORKS AS AN ANSWER
------------------------------
This demonstrates dynamic dispatch happening through a base-typed
variable with zero extra syntax, and explains it using the chapter's
own stated contrast -- Java's virtual-by-default instance methods
versus C++'s opt-in virtual keyword, which would change this exact
example's outcome if it were written in C++ without that keyword.