Part 1 — Definition

An Abstract Class is a restricted class that cannot be used to create objects. To access it, it must be inherited from another class. It can have both abstract methods (without a body) and regular methods (with a body).

Part 2 — Syntax

abstract class Animal {
    abstract void makeSound(); // No body
    void sleep() { System.out.println("Zzz"); }
}

Part 3 — Example

Problem: Create an abstract Bank class with a method to get interest rate.

abstract class Bank {
    abstract int getInterest();
}
class SBI extends Bank {
    int getInterest() { return 7; }
}

Part 4 — Video

Video: Coming Soon

Part 1 — Definition

An Interface is a completely "abstract class" that is used to group related methods with empty bodies. Interfaces are used to achieve abstraction and multiple inheritance in Java. A class implements an interface.

Part 2 — Syntax

interface Drawable {
    void draw(); // Implicitly public and abstract
}

class Circle implements Drawable {
    public void draw() { ... }
}

Part 3 — Example

Problem: Model a smartphone that acts as both a Camera and a Phone.

interface Camera { void takePhoto(); }
interface Phone { void call(); }

class SmartPhone implements Camera, Phone {
    public void takePhoto() { System.out.println("Click!"); }
    public void call() { System.out.println("Calling..."); }
}

Observation: A class can implement multiple interfaces, but can only extend one class.

Part 4 — Video

Video: Coming Soon