Polymorphism in Java

# CHAPTER 16

Polymorphism in Java #

1. Introduction #

2. Types of Polymorphism #

3. Compile-Time Polymorphism (Overloading) #

class Calculator {
    int add(int a, int b) { return a + b; }
    double add(double a, double b) { return a + b; }
    int add(int a, int b, int c) { return a + b + c; }
}

4. Runtime Polymorphism (Overriding) #

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

// Dynamic dispatch
Shape s1 = new Circle();
Shape s2 = new Square();
s1.draw(); // "Drawing a circle" — calls Circle's version at RUNTIME
s2.draw(); // "Drawing a square"

5. The instanceof Operator #

Shape s = new Circle();
System.out.println(s instanceof Circle); // true
System.out.println(s instanceof Shape);  // true
System.out.println(s instanceof Square); // false

6. Upcasting and Downcasting #

// Upcasting (automatic): Child → Parent
Shape shape = new Circle();

// Downcasting (manual): Parent → Child
Circle circle = (Circle) shape;  // Must be sure it's actually a Circle!

7. MCQ Quiz with Answers #

8. Interview Questions #

• Q: Explain compile-time vs runtime polymorphism.

• Q: What is dynamic method dispatch?

• Q: Can constructors be polymorphic?

• Q: What is the difference between method hiding and method overriding?

9. Summary #

10. Next Chapter Recommendation #