Class objects

Basic Structure of a Class

void main()

{

 var student1=Student(); //object of class Student

 print('${student1.id} and ${student1.name}');

}

//In Class- Define states(Properties) and behaviour of a student

class Student

{

 int? id;        //property of Student

 String? name;        //property of Student

 void study() //Behaviour of Student

 {

 }

 void sleep() //Behaviour of Student

 {

 }

}

Behaviour (Method) calling of a class

void main()

{

 var student1=Student();

 student1.id=1;

 student1.name='Sandeep';

 print('${student1.id} and ${student1.name}');

 student1.study();   //calling behavour/method

 student1.sleep();   //calling behavour/method

}

//In Class- Define states(Properties) and behaviour of a student

class Student

{

 int? id;        //property of Student

 String? name;        //property of Student

 void study() //Behaviour of Student

 {

   print('${this.name} is now studing');

 }

 void sleep() //Behaviour of Student

 {

   print('${this.name} will sleeping after 1 hour ');

 }

}

---------------------------------------------------------------------

1. Simple Class with Properties and Methods

class Rectangle 

{

 double width;

 double height;

 Rectangle(this.width, this.height);

 double calculateArea() {

   return width * height;

 }

 double calculatePerimeter() {

   return 2 * (width + height);

 }

}

void main() {

 Rectangle rect = Rectangle(5.0, 3.0);

 print('Area: ${rect.calculateArea()}');

 print('Perimeter: ${rect.calculatePerimeter()}');

}

-------------------------------------------------------------

void main()

{

 var student1=Student();  //one object, student1 is refrence varible

 student1.id=1;       

 student1.name='Sandeep';

 print('${student1.id} and ${student1.name}');

 student1.study();   //calling behavour/method

 student1.sleep();   //calling behavour/method

 var student2=Student();    //one object, student2 is refrence varible

 student2.id=2;

 student2.name='Pradeep';

 student2.age=23;

 print('${student2.id} and ${student2.name}');

 student2.study();

 student2.sleep();

 student2.intro();

}

//In Class- Define states(Properties) and behaviour of a student

class Student

{

 int? id;        //property of Student (instance or field variable)

 String? name;        //property of Student (instance or field variable)

 int? age;

 void study() //Behaviour of Student

 {

   print('${this.name} is now studing');

 }

 void sleep() //Behaviour of Student

 {

   print('${this.name} will sleeping after 1 hour ');

 }

 void intro()

 {

   print('${this.name} has age 24');

 }

}

A simple program that creates a Person class with a name and age, and prints a greeting.

class Person {

 String name;

 int age;

 Person(this.name, this.age); //constructure

 void greet() {

   print("Hello, my name is $name and I am $age years old.");

 }

}

void main() {

 Person person = Person("Alice", 25);

 person.greet();

}

2. Constructor with Default Values

A program with a constructor that provides default values if no values are passed.

class Car {

 String brand;

 int year;

 Car({this.brand = "Toyota", this.year = 2020}); //default constructor

 void displayInfo() {

   print("Brand: $brand, Year: $year");

 }

}

void main() {

 Car car1 = Car();

 Car car2 = Car(brand: "Honda", year: 2022);

 car1.displayInfo();

 car2.displayInfo();

}

3. Getter and Setter

A program that uses getter and setter methods to access private fields.

class Rectangle {

 double _width;

 double _height;

 Rectangle(this._width, this._height);

 double get area => _width * _height;

 set width(double value) => _width = value;

 set height(double value) => _height = value;

}

void main() {

 Rectangle rect = Rectangle(5.0, 4.0);

 print("Area: ${rect.area}");

 rect.width = 6.0;

 print("New Area: ${rect.area}");

}

4. Using Inheritance

A program demonstrating inheritance with a parent Animal class and a child Dog class.

class Animal {

 void sound() {

   print("Animal makes a sound.");

 }

}

class Dog extends Animal {

 @override

 void sound() {

   print("Dog barks.");

 }

}

void main() {

 Dog dog = Dog();

 dog.sound();

}

5. Method Overriding

A program that overrides a parent method in the child class.

class Vehicle {

 void start() {

   print("Vehicle starting...");

 }

}

class Car extends Vehicle {

 @override

 void start() {

   print("Car starting with a roar...");

 }

}

void main() {

 Vehicle vehicle = Car();

 vehicle.start();

}

6. Abstract Class Example

A program using an abstract class with abstract and concrete methods.

abstract class Shape {

 void draw(); // Abstract method

 void printShape() {

   print("This is a shape.");

 }

}

class Circle extends Shape {

 @override

 void draw() {

   print("Drawing a circle.");

 }

}

void main() {

 Circle circle = Circle();

 circle.printShape();

 circle.draw();

}

7. Using Interface for Polymorphism

A program using an interface to define behavior that different classes can implement.

class Printable {

void printDetails();

}

class Book implements Printable {

 String title;

 Book(this.title);

 @override

 void printDetails() {

   print("Book title: $title");

 }

}

void main() {

 Printable printable = Book("Dart Programming");

 printable.printDetails();

}

8. Named Constructors

A program using named constructors to create different types of objects from the same class.

class Student {

 String name;

 int age;

 Student(this.name, this.age);

 // Named constructor

 Student.fromHighSchool() : name = "High School Student", age = 16;

 Student.fromUniversity() : name = "University Student", age = 20;

 void displayInfo() {

   print("Name: $name, Age: $age");

 }

}

void main() {

 Student student1 = Student.fromHighSchool();

 Student student2 = Student.fromUniversity();

 student1.displayInfo();

 student2.displayInfo();

}

9. Encapsulation with Private Variables

A program that uses encapsulation by making variables private and using getters and setters.

class BankAccount {

 double _balance;

 BankAccount(this._balance);

 double get balance => _balance;

 void deposit(double amount) {

   _balance += amount;

 }

 void withdraw(double amount) {

   if (amount <= _balance) {

     _balance -= amount;

   } else {

     print("Insufficient funds.");

   }

 }

}

void main() {

 BankAccount account = BankAccount(1000.0);

 account.deposit(500.0);

 account.withdraw(300.0);

 print("Balance: ${account.balance}");

}

10. Static Variables and Methods

A program that demonstrates the use of static variables and methods in a class.

class MathUtils {

 static const double pi = 3.14159;

 static double areaOfCircle(double radius) {

   return pi * radius * radius;

 }

}

void main() {

 print("PI: ${MathUtils.pi}");

 print("Area of circle with radius 5: ${MathUtils.areaOfCircle(5)}");

}

These programs cover basic principles of classes, objects, encapsulation, inheritance, polymorphism, abstraction, and static members in Dart. Each example provides a glimpse into how Dart handles these object-oriented concepts.

Summary of Concepts:

1. Basic class definition and constructors.

2. Inheritance and method overriding.

3. Getter, setter, and factory constructors.

4. Polymorphism, interfaces, and abstract classes.

5. Static methods, instance methods, and collections.

6. Enums and event handling in object-oriented design

1. Simple Class Definition

class Person {

 String name;

 int age;

 Person(this.name, this.age);

 void introduce() {

   print("Hi, my name is $name and I am $age years old.");

 }

}

void main() {

 var person = Person("Alice", 25);

 person.introduce();  // Output: Hi, my name is Alice and I am 25 years old.

}

2. Class with Constructor Overloading

class Rectangle {

 double width;

 double height;

 // Constructor 1

 Rectangle(this.width, this.height);

 // Constructor 2 (named constructor)

 Rectangle.square(double size) : width = size, height = size;

 double area() => width * height;

}

void main() {

 var rect1 = Rectangle(5, 10);

 var square = Rectangle.square(4);

 print("Area of rectangle: ${rect1.area()}"); // Output: 50

 print("Area of square: ${square.area()}");   // Output: 16

}

3. Getter and Setter Methods

class Circle {

 double radius;

 Circle(this.radius);

 // Getter

 double get area => 3.14 * radius * radius;

 // Setter

 set radiusValue(double value) {

   if (value > 0) {

     radius = value;

   } else {

     print("Radius cannot be negative.");

   }

 }

}

void main() {

 var circle = Circle(5);

 print("Area: ${circle.area}");  // Output: 78.5

 circle.radiusValue = 10;

 print("Updated Area: ${circle.area}");  // Output: 314.0

}

4. Inheritance

class Animal {

 void speak() {

   print("Animal makes a sound.");

 }

}

class Dog extends Animal {

 @override

 void speak() {

   print("Dog barks.");

 }

}

void main() {

 var dog = Dog();

 dog.speak(); // Output: Dog barks.

}

5. Method Overriding

class Employee {

 void work() {

   print("Employee is working.");

 }

}

class Manager extends Employee {

 @override

 void work() {

   print("Manager is managing the team.");

 }

}

void main() {

 var manager = Manager();

 manager.work();  // Output: Manager is managing the team.

}

6. Polymorphism

class Shape {

 void draw() {

   print("Drawing a shape.");

 }

}

class Circle extends Shape {

 @override

 void draw() {

   print("Drawing a circle.");

 }

}

void main() {

 Shape shape = Circle();

 shape.draw(); // Output: Drawing a circle.

}

7. Abstract Class

abstract class Vehicle {

 void start();  // Abstract method

}

class Car extends Vehicle {

 @override

 void start() {

   print("Car is starting.");

 }

}

void main() {

 var car = Car();

 car.start(); // Output: Car is starting.

}

8. Interface Implementation

class Animal {

 void sound();

}

class Cat implements Animal {

 @override

 void sound() {

   print("Meow");

 }

}

void main() {

 var cat = Cat();

 cat.sound();  // Output: Meow

}

9. Static Methods

class MathUtility {

 static int add(int a, int b) {

   return a + b;

 }

}

void main() {

 print(MathUtility.add(5, 3));  // Output: 8

}

10. Class with List of Objects

class Student {

 String name;

 int grade;

 Student(this.name, this.grade);

}

void main() {

 var students = [

   Student("Alice", 90),

   Student("Bob", 85),

   Student("Charlie", 95)

 ];

 for (var student in students) {

   print("${student.name}: ${student.grade}");

 }

}

11. Constructor with Default Values

class Point {

 double x, y;

 // Constructor with default values

 Point([this.x = 0, this.y = 0]);

 void display() {

   print("Point is at ($x, $y)");

 }

}

void main() {

 var p1 = Point();

 var p2 = Point(2, 3);

 p1.display();  // Output: Point is at (0.0, 0.0)

 p2.display();  // Output: Point is at (2.0, 3.0)

}

12. Factory Constructor

class Shape {

 String type;

 // Named factory constructor

 Shape._(this.type);

 factory Shape.circle() {

   return Shape._("Circle");

 }

 factory Shape.square() {

   return Shape._("Square");

 }

 void display() {

   print("This is a $type.");

 }

}

void main() {

 var shape1 = Shape.circle();

 var shape2 = Shape.square();

 shape1.display();  // Output: This is a Circle.

 shape2.display();  // Output: This is a Square.

}

13. Class with Map

class Employee {

 String name;

 int id;

 Employee(this.name, this.id);

 Map<String, dynamic> toJson() {

   return {

     'name': name,

     'id': id,

   };

 }

}

void main() {

 var emp = Employee("Alice", 101);

 print(emp.toJson());  // Output: {name: Alice, id: 101}

}

14. Nested Classes

class Outer {

 String name;

 Outer(this.name);

 class Inner {

 void display() {

 print("This is an inner class.");

 }

 }

}

void main() {

 var outer = Outer("Outer Class");

 var inner = outer.Inner();

 inner.display(); // Output: This is an inner class.

}

15. Instance Variables vs Static Variables

class Counter

{

 int _count = 0; // Instance variable

 static int staticCount = 0; // Static variable

 void increment() {

   _count++;

   staticCount++;

 }

 void display() {

   print("Instance count: $_count");

   print("Static count: $staticCount");

 }

}

void main() {

 var counter1 = Counter();

 var counter2 = Counter();

 counter1.increment();

 counter2.increment();

 counter1.display();

 counter2.display();

}

16. Class with List of Objects and Methods

class Book {

 String title;

 String author;

 Book(this.title, this.author);

 void display() {

   print("$title by $author");

 }

}

void main() {

 var books = [

   Book("1984", "George Orwell"),

   Book("To Kill a Mockingbird", "Harper Lee")

 ];

 for (var book in books) {

   book.display();

 }

}

17. Class with Set Operations

class CollectionExample {

 Set<int> numbers;

 CollectionExample() : numbers = {};

 void addNumber(int number) {

   numbers.add(number);

 }

 void displayNumbers() {

   print(numbers);

 }

}

void main() {

 var collection = CollectionExample();

 collection.addNumber(1);

 collection.addNumber(2);

 collection.addNumber(2);

 collection.displayNumbers();  // Output: {1, 2}

}

18. Class with Methods and Arguments

class Calculator {

 double add(double a, double b) => a + b;

 double subtract(double a, double b) => a - b;

 double multiply(double a, double b) => a * b;

 double divide(double a, double b) => a / b;

}

void main() {

 var calc = Calculator();

 print(calc.add(10, 5)); // Output: 15

 print(calc.subtract(10, 5)); // Output: 5

}

19. Using Class with Enum

enum Status { Active, Inactive }

class User {

 String name;

 Status status;

 User(this.name, this.status);

 void display() {

   print("User: $name, Status: ${status.toString().split('.').last}");

 }

}

void main() {

 var user1 = User("Alice", Status.Active);

 var user2 = User("Bob", Status.Inactive);

 user1.display();  // Output: User: Alice, Status: Active

 user2.display();  // Output: User: Bob, Status: Inactive

}

20. Using a Class for Event Handling

class Event {

 String name;

 Event(this.name);

 void trigger() {

   print("$name event triggered!");

 }

}

void main() {

 var event1 = Event("Login");

 var event2 = Event("Logout");

 event1.trigger();  // Output: Login event triggered!

 event2.trigger();  // Output: Logout event triggered!

}