🏗️ Lesson 5: Object-Oriented Basics

⏱ 35-45 min 📊 Intermediate 🏗️ Project-Based 🔥 Core Concept 2026 🔗 Official Source

🏗️

Why Object-Oriented Programming?

Imagine building with LEGO blocks. Each block is a self-contained "object" with its own properties and behaviors. OOP lets you build complex programs the same way!

🏠

Class = Blueprint

A plan that describes how to build something

🏡

Object = Actual House

A real instance built from the blueprint

📋

Properties = Features

Color, size, number of rooms

🔧

Methods = Actions

Open door, turn on lights, heat water

🎯

Today's Project: "Zoo Management System"

We'll build a complete zoo management application:

🐾 Animal class hierarchy (inheritance)
🏗️ Different animal types (Mammal, Bird, Reptile)
🎵 Each animal makes its own sound (polymorphism)
📊 Zoo statistics and reporting
🔧 Professional class design patterns

Step 1

Anatomy of a Class

🔍 Interactive Class Dissector

Animal

Properties

📝 name: String

🔢 age: int

🐾 species: String

Methods

🏗️ Animal(name, age, species)

🔊 makeSound()

📋 get description

🍽️ eat(food)

👆 Click on any property or method to learn more!

✏️ Live Class Builder

Class Name: Properties (comma-separated name:type): Methods (comma-separated):

📄 Generated Class Code

class Animal {
  String name;
  int age;
  String species;
  
  Animal(this.name, this.age, this.species);
  
  void makeSound() {
    print('$name makes a sound');
  }
  
  void eat(String food) {
    print('$name eats $food');
  }
  
  void sleep() {
    print('$name is sleeping');
  }
}

Step 2

Constructors: Building Objects

🏗️ Constructor Types Visualizer

Default Constructor

class Animal {
  String name;
  int age;
  
  // Default constructor
  Animal(this.name, this.age);
}

// Usage
var cat = Animal('Whiskers', 3);

Named Constructor

class Animal {
  String name;
  int age;
  
  Animal(this.name, this.age);
  
  // Named constructor
  Animal.newborn(this.name) : age = 0;
  
  Animal.unknown() 
    : name = 'Unknown',
      age = 0;
}

Factory Constructor

class Animal {
  String name;
  int age;
  static final Map<String, Animal> _cache = {};
  
  Animal._internal(this.name, this.age);
  
  factory Animal(String name, int age) {
    return _cache.putIfAbsent(
      name, 
      () => Animal._internal(name, age)
    );
  }
}

Factory constructors can return cached instances!

Constant Constructor

class Point {
  final int x;
  final int y;
  
  const Point(this.x, this.y);
}

// Compile-time constants
const origin = Point(0, 0);
const unit = Point(1, 1);

Constant constructors create compile-time constants!

Step 3

Inheritance: Building Hierarchies

🌳 Interactive Inheritance Tree

🐾 Animal

🐕 Mammal

🦮 Dog

🐱 Cat

🐦 Bird

🦜 Parrot

🦅 Eagle

📋 Class Details

Click on any class to see its details!

📊 Before vs After Inheritance

❌ Without Inheritance

class Dog {
  String name;
  int age;
  void eat() { ... }
  void sleep() { ... }
  void bark() { ... }
}

class Cat {
  String name;
  int age;
  void eat() { ... }
  void sleep() { ... }
  void meow() { ... }
}

😰 Duplicated code everywhere!

✅ With Inheritance

class Animal {
  String name;
  int age;
  void eat() { ... }
  void sleep() { ... }
}

class Dog extends Animal {
  void bark() { ... }
}

class Cat extends Animal {
  void meow() { ... }
}

😍 Clean & reusable!

Step 4

Polymorphism: Many Forms

🎭 Polymorphism in Action

Create Animals:

Make All Animals Speak:

Add animals and make them speak!

🦁 Your Zoo:

No animals yet...

Step 5

Abstract Classes & Interfaces

📜 Abstract Class Contract

Abstract Class (Contract)

abstract class Shape {
  double get area;
  double get perimeter;
  
  void display() {
    print('Area: $area');
    print('Perimeter: $perimeter');
  }
}

Implementations

🔵 Circle

class Circle extends Shape {
  double radius;
  Circle(this.radius);
  
  double get area => pi * radius * radius;
  double get perimeter => 2 * pi * radius;
}

🟦 Rectangle

class Rectangle extends Shape {
  double width, height;
  Rectangle(this.width, this.height);
  
  double get area => width * height;
  double get perimeter => 2 * (width + height);
}

🏆

Build: Zoo Management System

🐾 Base Animal Class

🏛️ Zoo Management Class

🎮 Main Program

📤 Program Output Preview

Edit the code to see the output!

🎮 OOP Challenge: Concept Master Quiz

🏆 Score: 0/5

⚡ Streak: 0

⏱ Time: 0s

🎯 Accuracy: 100%