Objective:
Learn inheritance, polymorphism, abstraction, and encapsulation.
Practice by creating small projects based on OOP concepts.
1. Inheritance
Inheritance allows a class to inherit properties and methods from another class.
class Animal {
String name;
Animal(this.name);
void eat() {
print('$name is eating');
}
}
class Dog extends Animal {
Dog(String name) : super(name);
void bark() {
print('$name is barking');
}
}
void main() {
Dog dog = Dog('Buddy');
dog.eat();
dog.bark();
}
Explanation:
Animal is the parent class with a property name and a method eat.
Dog is the child class that extends Animal and inherits its properties and methods.
The Dog class also has its own method bark.
Diagram:
2. Polymorphism
Polymorphism allows objects to be treated as instances of their parent class rather than their actual class.
class Animal {
void sound() {
print('Animal makes a sound');
}
}
class Dog extends Animal {
@override
void sound() {
print('Dog barks');
}
}
class Cat extends Animal {
@override
void sound() {
print('Cat meows');
}
}
void main() {
Animal myDog = Dog();
Animal myCat = Cat();
myDog.sound();
myCat.sound();
}
Explanation:
The Animal class has a method sound.
The Dog and Cat classes override the sound method.
Polymorphism allows calling the sound method on Animal references, which results in calling the overridden methods in Dog and Cat.
Diagram:
3. Abstraction
Abstraction allows defining methods without implementing them, using abstract classes and methods.
abstract class Shape {
void draw();
}
class Circle extends Shape {
@override
void draw() {
print('Drawing a circle');
}
}
class Rectangle extends Shape {
@override
void draw() {
print('Drawing a rectangle');
}
}
void main() {
Shape circle = Circle();
Shape rectangle = Rectangle();
circle.draw();
rectangle.draw();
}
Explanation:
Shape is an abstract class with an abstract method draw.
Circle and Rectangle classes extend Shape and implement the draw method.
Abstract classes cannot be instantiated, but they can be used as reference types.
Diagram:
4. Encapsulation
Encapsulation restricts access to certain properties and methods using access modifiers.
class BankAccount {
String _accountNumber;
double _balance;
BankAccount(this._accountNumber, this._balance);
String get accountNumber => _accountNumber;
double get balance => _balance;
void deposit(double amount) {
if (amount > 0) {
_balance += amount;
}
}
void withdraw(double amount) {
if (amount > 0 && amount <= _balance) {
_balance -= amount;
}
}
}
void main() {
BankAccount account = BankAccount('123456', 1000.0);
account.deposit(500.0);
print('Balance: ${account.balance}');
account.withdraw(200.0);
print('Balance: ${account.balance}');
}
Explanation:
The BankAccount class encapsulates the properties _accountNumber and _balance by making them private.
Public getters provide read-only access to the properties.
Methods deposit and withdraw allow controlled modification of the balance.
Diagram:
5. Small Project: Library Management System
Project Objective:
- Create a simple library management system using advanced OOP concepts.
Project Requirements:
Define a Book class with properties like title, author, and ISBN.
Define a Member class with properties like name, member ID, and a list of borrowed books.
Define a Library class with methods to add books, register members, lend books, and return books.
Code Implementation:
class Book {
String title;
String author;
String isbn;
Book(this.title, this.author, this.isbn);
}
class Member {
String name;
String memberId;
List<Book> borrowedBooks = [];
Member(this.name, this.memberId);
void borrowBook(Book book) {
borrowedBooks.add(book);
}
void returnBook(Book book) {
borrowedBooks.remove(book);
}
}
class Library {
List<Book> books = [];
List<Member> members = [];
void addBook(Book book) {
books.add(book);
}
void registerMember(Member member) {
members.add(member);
}
void lendBook(String isbn, String memberId) {
Book? book = books.firstWhere((book) => book.isbn == isbn, orElse: () => null);
Member? member = members.firstWhere((member) => member.memberId == memberId, orElse: () => null);
if (book != null && member != null) {
member.borrowBook(book);
books.remove(book);
print('${member.name} borrowed ${book.title}');
} else {
print('Book or Member not found');
}
}
void returnBook(String isbn, String memberId) {
Member? member = members.firstWhere((member) => member.memberId == memberId, orElse: () => null);
if (member != null) {
Book? book = member.borrowedBooks.firstWhere((book) => book.isbn == isbn, orElse: () => null);
if (book != null) {
member.returnBook(book);
books.add(book);
print('${member.name} returned ${book.title}');
} else {
print('Book not found in borrowed books');
}
} else {
print('Member not found');
}
}
}
void main() {
Library library = Library();
library.addBook(Book('Dart Programming', 'John Doe', '123'));
library.addBook(Book('Flutter Development', 'Jane Smith', '456'));
library.registerMember(Member('Alice', '001'));
library.registerMember(Member('Bob', '002'));
library.lendBook('123', '001');
library.returnBook('123', '001');
}
Explanation:
The Book class represents a book with properties title, author, and isbn.
The Member class represents a library member with properties name, memberId, and a list of borrowed books. It has methods to borrow and return books.
The Library class manages the collection of books and members. It has methods to add books, register members, lend books, and return books.
The main function demonstrates adding books to the library, registering members, lending books, and returning books.
Diagram:
By practicing these advanced OOP concepts, you will gain a deeper understanding of how to structure and organize your Dart programs effectively. Happy coding!
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