Java Polymorphism

public class Overloading {

    // Same method name, different parameter types/count
    public static void print(int n) {
        System.out.println("int: " + n);
    }

    public static void print(double d) {
        System.out.println("double: " + d);
    }

    public static void print(String s) {
        System.out.println("String: " + s);
    }

    public static void print(int a, int b) {
        System.out.println("two ints: " + a + ", " + b);
    }

    public static void main(String[] args) {
        print(42);          // int: 42
        print(3.14);        // double: 3.14
        print("Hello");     // String: Hello
        print(1, 2);        // two ints: 1, 2
        // The compiler picks the right version at compile time
    }
}

class Shape {
    public void draw() {
        System.out.println("Drawing a shape.");
    }
}

class Circle extends Shape {
    @Override
    public void draw() {
        System.out.println("Drawing a circle.");
    }
}

class Rectangle extends Shape {
    @Override
    public void draw() {
        System.out.println("Drawing a rectangle.");
    }
}

class Triangle extends Shape {
    @Override
    public void draw() {
        System.out.println("Drawing a triangle.");
    }
}

public class RuntimePoly {
    public static void main(String[] args) {
        // Upcasting — parent reference, child object
        Shape s1 = new Circle();
        Shape s2 = new Rectangle();
        Shape s3 = new Triangle();

        // JVM calls the correct overridden method at runtime
        s1.draw();  // Drawing a circle.
        s2.draw();  // Drawing a rectangle.
        s3.draw();  // Drawing a triangle.

        // Polymorphic array
        Shape[] shapes = { new Circle(), new Rectangle(), new Triangle() };
        for (Shape s : shapes) {
            s.draw();  // dynamic dispatch

            // instanceof check before downcasting
            if (s instanceof Circle c) {
                System.out.println("  -> This is a Circle");
            }
        }
    }
}