Class & Object in Dart

Class:-A class is a blueprint used to create objects. It contains a collection of methods (functions) and properties (attributes) that define the characteristics and behaviors of the object.
OR
A class can be understood as a blueprint or a template used to create objects. It defines a specific data structure that encapsulates data (attributes or properties) and methods (functions or behaviors). A class specifies how the data will be structured and how we can interact with it — although the class itself does not hold any actual data.

About Bulueprint:- A blueprint is a predefined structure or detailed design that defines how an object will be created — what attributes (properties) and methods (behaviors) it will have. It does not hold any real data itself, but it can be used to create multiple real-world instances (objects).

Real Example:-
🚗 Real-Life Analogy: Car Factory & Blueprint
Imagine there’s a Car Factory that wants to manufacture different types of cars.
Before building any actual car, the factory creates a design document — also known as a blueprint. This blueprint defines all the essential characteristics a car should have:

• 4 wheels
• 1 engine
• A color
• A driving mechanism
• A braking system

This blueprint is not a real car — it doesn’t move or take passengers. But it holds the structure and instructions needed to create multiple real cars based on the same design.

You can build:

• A red car
• A blue car
• An electric car
• A sports car

Each of them follows the same blueprint but may differ in actual features or configurations.In object-oriented programming, this blueprint is the class, and the real cars are the objects.
Syntax:-

class_keyword ClassName {
    // Constructors
    // Properties (fields)
    // Methods(Functions)
}

Examples:-

// 1. Animal class
class Animal {
    // Properties and Methods
}

// 2. Dog class
class Dog {
  
    void bark() {
       print("Dog is barking");
    }
}

// 3. Student class
class Student {
    String name="Raman";
 
    void study() {
       print("$name is studying");
    }
}

// 4. BankAccount class
class BankAccount {
    String accountHolder="Raman";
    double balance=10000.00;

    void showBalance() {
        print("Balance: $balance");
    }
}

Object:- An object is an instance of a class that combines properties (attributes) and methods (behaviors).
It represents real-world entities — like Student, Car, Mobile, etc.

Get Ajay kumar’s stories in your inbox

Join Medium for free to get updates from this writer.

Remember me for faster sign in

Each object has three key characteristics:

1. State:
   Represents the current data or condition of the object.
   Example: A student’s name = “Raman”, age = 23.
2. Behavior:
   Describes what the object can do or what actions it can perform.
   Example: A student can study(), attendClass(), etc.
3. Identity:
   Every object has a unique name or reference through which it can be identified.
   Example: Student s1 = new Student(); — here, s1 is the identity of the object.

Instance:- An instance means a “real copy or example of a class.”

Car car = Car(); // car is an Object.

Real Example:-

Imagine you have a car design (class) that says — 4 wheels, 1 engine, and a brake system.
Now, when a factory uses that design to build a real car, that real car is called an instance. So, a class is the design, and an instance is the actual object built from that design.

How to create properties in a class

1. Student Class with Single Property

class Student {
  String name = "Raman"; 
}

2. Car Class with Multiple Properties

class Car {
  String brand = "Tesla";
  int speed = 120;
  String color = "Red";
}

3. Light Class with Single Property

class Light {
  bool isOn = false; 
}

4. Circle Class with Single Property

class Circle {
  double radius = 5.0;
}

5. School class Single Property

class School {
  List<String> subjects = ["Math", "Science", "English"];
}

6. Country Class with Single Property

class Country {
  Map<String, String> states = {
    "UP": "Lucknow",
    "Bihar": "Patna",
  };
}

How to create methods in a class

1. Student Class with Single Method

class Student {
  void study() {
    print("Studying...");
  }
}


2. Calculator Class with single Method

class Calculator {
  void add(int a, int b) {
    print("Sum = ${a + b}");
  }
}

3. NumberCheck Class with Single Method

class NumberCheck {
  String checkEvenOdd(int n) {
    if (n % 2 == 0) {
      return "Even";
    } else {
      return "Odd";
    }
  }
}

4. Marks Class with single method

class Marks {
  List<int> getMarks() {
    return [90, 85, 78];
  }
}

5. Calculator class  with multiple methods

class Calculator{

void add(){
print(10+100);
           }
void substraction(){
  print(20-10);
                   }
                  }

How to Create an Object and Access properties & Methods from a Class

Meaning of Access:- Access means the ability to use, read, or interact with something.
In programming:

• Accessing a property → means reading or modifying the value of a variable inside a class/object.
• Accessing a method → means calling or invoking the function that belongs to a class/object.

Examples:-

1. Car Class 
class Car {
  String brand = "Tesla";
  int speed = 120;

  void showDetails() {
    print("Brand: $brand, Speed: $speed km/h");
  }
}

void main() {
  var car1 = Car();      // create object
  print(car1.brand);     // access property
  print(car1.speed);     // access property
  car1.showDetails();    // access method
}
2. Student Class

class Student {
  String name = "Raman";
  int age = 21;

  void showDetails() {
    print("Name: $name, Age: $age");
  }
}

void main() {
  var s1 = Student();     // create object
  print(s1.name);         // access property
  print(s1.age);          // access property
  s1.showDetails();       // access method
}

3. Mobile Class 

 class Mobile {
  String brand = "Samsung";
  double price = 25000;

  void showDetails() {
    print("Brand: $brand, Price: ₹$price");
  }
}

void main() {
  var m1 = Mobile();      // create object
  print(m1.brand);        // access property
  print(m1.price);        // access property
  m1.showDetails();       // access method
}

4. Book Class 

  class Book {
  String title = "Flutter Guide";
  String author = "John Smith";

  void showDetails() {
    print("Title: $title, Author: $author");
  }
}

void main() {
  var b1 = Book();        // create object
  print(b1.title);        // access property
  print(b1.author);       // access property
  b1.showDetails();       // access method
}

Meaning of (.) Dot Operator:-

• The dot (.) is used to access members of a class (properties and methods) through an object.
• It connects the object with its data (variables) and behavior (functions).