Abstract Classes

1. Welcome and Icebreaker:

• If you could design a blueprint for any kind of object, what would it be?

2. Outline the Session:

• We’ll learn about abstract classes in TypeScript: what they are, how to use them, and why they’re useful.
• Learning Outcomes: Understand how to define abstract classes and methods, and how to implement them in subclasses.
• Let’s get abstract!

3. Concept Explanation:

• Abstract Classes are classes that cannot be instantiated directly. They are meant to be extended by other classes.
• Abstract classes can have both implemented methods and abstract methods (methods without a body).
• Subclasses must implement all abstract methods.
• Use the abstract keyword for both classes and methods.

4. Live Coding Demonstration:

abstract class Shape {
  abstract getArea(): number;
  describe() {
    console.log(`This shape has an area of ${this.getArea()}`);
  }
}

class Circle extends Shape {
  radius: number;
  constructor(radius: number) {
    super();
    this.radius = radius;
  }
  getArea(): number {
    return Math.PI * this.radius * this.radius;
  }
}

const circle = new Circle(5);
circle.describe(); // This shape has an area of 78.53981633974483
// const shape = new Shape(); // Error: Cannot create an instance of an abstract class.

5. Tasks:

• Short Exercise:
  1. Create an abstract class Animal with an abstract method makeSound() and a concrete method move() that prints a message.
  2. Create a subclass Cat that implements makeSound().
  3. Create an instance of Cat and call both methods.