Today, we will explore advanced Object-Oriented Programming (OOP) concepts in Dart by building a Library Management System. This project will incorporate various OOP principles such as inheritance, encapsulation, polymorphism, abstract classes, interfaces, mixins, static members, and getters/setters. By the end of this day, you should have a solid understanding of how to create classes and objects in Dart, use constructors, and apply various OOP concepts. These skills are fundamental for developing robust applications in Flutter.
Inheritance allows a class to inherit properties and methods from another class, promoting code reusability.
class Item {
void display() {
print('This is an item');
}
}
class Book extends Item {
String title;
String author;
Book(this.title, this.author);
@override
void display() {
print('Title: $title, Author: $author');
}
}- Encapsulation: Encapsulation hides the internal state of an object and requires all interaction to be performed through an object's methods.
Example
class Member {
String _name; // Private property
Member(this._name);
String get name => _name; // Getter
set name(String name) => _name = name; // Setter
}
void main() {
Member member = Member('Alice');
print(member.name); // Output: Alice
member.name = 'Bob';
print(member.name); // Output: Bob
}- Polymorphism: Polymorphism allows methods to perform different tasks based on the object they are acting upon.
Example
abstract class LibraryItem {
void checkOut();
}
class Book extends LibraryItem {
String title;
Book(this.title);
@override
void checkOut() {
print('Checking out book: $title');
}
}
class DVD extends LibraryItem {
String title;
DVD(this.title);
@override
void checkOut() {
print('Checking out DVD: $title');
}
}
void main() {
List<LibraryItem> items = [Book('1984'), DVD('Inception')];
for (var item in items) {
item.checkOut();
}
}- Abstract Classes and Interfaces: Abstract classes cannot be instantiated and are often used to define a blueprint for other classes.
Example
abstract class DataSource {
void fetchData();
}
class LocalDataSource implements DataSource {
@override
void fetchData() {
print('Fetching data from local source');
}
}
class RemoteDataSource implements DataSource {
@override
void fetchData() {
print('Fetching data from remote source');
}
}- Mixins: Mixins allow you to reuse a class's code in multiple class hierarchies.
Example
mixin Auditable {
void audit() {
print('Audit log created');
}
}
class LibraryItem with Auditable {}
void main() {
LibraryItem item = LibraryItem();
item.audit(); // Output: Audit log created
}- Static Members: Static members belong to the class rather than to any specific object.
Example
class LibraryUtils {
static int calculateLateFee(int daysLate) {
return daysLate * 2;
}
}
void main() {
print(LibraryUtils.calculateLateFee(3)); // Output: 6
}- Getters and Setters: Getters and setters provide a way to access and modify the properties of an object.
Example
class Library {
String _name;
List<Book> _books;
Library(this._name, this._books);
String get name => _name;
set name(String value) => _name = value;
List<Book> get books => _books;
set books(List<Book> value) => _books = value;
}- Complete Project: Library Management System
// Define a class for books
class Book extends LibraryItem {
String title;
String author;
Book(this.title, this.author);
@override
void display() {
print('Book Title: $title, Author: $author');
}
}
// Define a class for DVDs
class DVD extends LibraryItem {
String title;
DVD(this.title);
@override
void display() {
print('DVD Title: $title');
}
}
// Define a class for magazines
class Magazine extends LibraryItem {
String title;
Magazine(this.title);
@override
void display() {
print('Magazine Title: $title');
}
}
// Define an abstract class for library items
abstract class LibraryItem {
void display();
}
// Define a mixin for auditing
mixin Auditable {
void audit() {
print('Audit log created');
}
}
// Define a class for library items with auditing
class AuditableLibraryItem with Auditable {}
// Define a class for library utilities
class LibraryUtils {
static int calculateLateFee(int daysLate) {
return daysLate * 2;
}
}
// Define a class for library members
class Member {
String _name; // Private property
Member(this._name);
String get name => _name; // Getter
set name(String name) => _name = name; // Setter
}
// Define a class for the library
class Library {
String _name;
List<LibraryItem> _items;
Library(this._name, this._items);
// Named constructor
Library.empty(this._name) : _items = [];
// Getter for name
String get name => _name;
set name(String value) => _name = value;
// Getter for items
List<LibraryItem> get items => _items;
set items(List<LibraryItem> value) => _items = value;
// Method to add a library item
void addItem(LibraryItem item) {
_items.add(item);
}
// Method to show library items
void showItems() {
print('Library: $_name');
for (var item in _items) {
item.display();
}
}
}
// Define abstract class for data source
abstract class DataSource {
void fetchData();
}
// Define local data source implementing data source
class LocalDataSource implements DataSource {
@override
void fetchData() {
print('Fetching data from local source');
}
}
// Define remote data source implementing data source
class RemoteDataSource implements DataSource {
@override
void fetchData() {
print('Fetching data from remote source');
}
}
// Main function to demonstrate the library management system
void main() {
// Creating books
Book book1 = Book('1984', 'George Orwell');
Book book2 = Book('To Kill a Mockingbird', 'Harper Lee');
// Creating DVDs
DVD dvd1 = DVD('Inception');
DVD dvd2 = DVD('The Matrix');
// Creating magazines
Magazine magazine1 = Magazine('Time');
Magazine magazine2 = Magazine('National Geographic');
// Creating a library
Library library = Library('City Library', [book1, book2, dvd1, dvd2, magazine1, magazine2]);
// Adding a new book
Book book3 = Book('Brave New World', 'Aldous Huxley');
library.addItem(book3);
// Displaying library items
library.showItems();
// Using mixin
AuditableLibraryItem item = AuditableLibraryItem();
item.audit(); // Output: Audit log created
// Static member usage
print('Late fee for 3 days: \$${LibraryUtils.calculateLateFee(3)}'); // Output: 6
// Inheritance and polymorphism
List<LibraryItem> items = [book1, dvd1, magazine1];
for (var item in items) {
item.display();
}
// Data sources
DataSource local = LocalDataSource();
DataSource remote = RemoteDataSource();
local.fetchData(); // Output: Fetching data from local source
remote.fetchData(); // Output: Fetching data from remote source
}Output
Library: City Library
Book Title: 1984, Author: George Orwell
Book Title: To Kill a Mockingbird, Author: Harper Lee
DVD Title: Inception
DVD Title: The Matrix
Magazine Title: Time
Magazine Title: National Geographic
Book Title: Brave New World, Author: Aldous Huxley
Audit log created
Late fee for 3 days: $6
Book Title: 1984, Author: George Orwell
DVD Title: Inception
Magazine Title: Time
Fetching data from local source
Fetching data from remote source#Dart #OOP #Flutter #Classes #Objects #Constructors #Inheritance #Polymorphism #Encapsulation #Abstraction #Mixins #LibraryManagementSystem