Learn how to identify Classes in Object-Oriented Programming

Introduction

In Object-Oriented Programming (OOP), identifying classes is a crucial skill that forms the foundation of good software design. This tutorial will guide you through the process of identifying classes using a simple, real-world example.

What is a Class?

A class is a blueprint for creating objects. It encapsulates data and behavior that are related to a specific concept or entity in your program.

Steps to Identify Classes

1. Identify the nouns in the problem description
2. Determine which nouns represent unique entities
3. Consider the attributes (properties) of each entity
4. Identify the behaviors (methods) associated with each entity

Example: Library Management System

Let’s use a simple library management system as our example. Here’s a basic description:

“A library has books and members. Members can borrow and return books. Each book has a title, author, and ISBN. Members have a name, ID, and can check out up to 3 books at a time.”

Step 1: Identify Nouns

From the description, we can identify the following nouns:

• Library
• Book
• Member
• Title
• Author
• ISBN
• Name
• ID

Step 2: Determine Unique Entities

From these nouns, we can identify two main entities that could be classes:

• Book
• Member

Note: Library could also be a class, but for this simple example, we’ll focus on Book and Member.

Step 3: Consider Attributes

For each class, let’s identify the attributes:

Attributes of Book class Objects:

• title
• author
• isbn

Attributes of Member Class Objects:

• name
• id
• borrowedBooks (a list of books currently borrowed)

Step 4: Identify Behaviors

Now, let’s identify the behaviors for each class:

Behaviors of Book Class Objects:

• No specific behaviors in this simple example

Bhaviors of Member Class Objects:

• borrowBook(book)
• returnBook(book)

Implementing the Classes

Now that we’ve identified our classes, attributes, and behaviors, let’s implement them in C++:

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;

class Book {
private:
    string title;
    string author;
    string isbn;

public:
    Book(string title, string author, string isbn)
        : title(title), author(author), isbn(isbn) {}

    string getTitle() const { return title; }
    string getAuthor() const { return author; }
    string getIsbn() const { return isbn; }

    friend ostream& operator<<(ostream& os, const Book& book) {
        os << book.title << " by " << book.author;
        return os;
    }
};

class Member {
private:
    string name;
    string id;
    vector<Book> borrowedBooks;

public:
    Member(string name, string id) : name(name), id(id) {}

    void borrowBook(const Book& book) {
        if (borrowedBooks.size() < 3) {
            borrowedBooks.push_back(book);
            cout << name << " has borrowed " << book << endl;
        } else {
            cout << name << " cannot borrow more books. Please return a book first." << endl;
        }
    }

    void returnBook(const Book& book) {
        auto it = find_if(borrowedBooks.begin(), borrowedBooks.end(),
            [&book](const Book& b) { return b.getIsbn() == book.getIsbn(); });

        if (it != borrowedBooks.end()) {
            borrowedBooks.erase(it);
            cout << name << " has returned " << book << endl;
        } else {
            cout << name << " did not borrow " << book << endl;
        }
    }
};

int main() {
    Book book1("The Great Gatsby", "F. Scott Fitzgerald", "9780743273565");
    Book book2("To Kill a Mockingbird", "Harper Lee", "9780446310789");

    Member member1("Alice", "M001");

    member1.borrowBook(book1);
    member1.borrowBook(book2);
    member1.returnBook(book1);

    return 0;
}

Conclusion

Identifying classes is a skill that improves with practice. Always start by analyzing the problem description, identifying key entities, their attributes, and behaviors. Remember, good class design leads to more maintainable and extensible code.

As you become more experienced, you’ll also learn to identify relationships between classes, such as inheritance or composition, which can further improve your object-oriented designs.