Introduction to Classes in Object-Oriented Programming

Understanding Classes in Object-Oriented Programming (OOP)

Object-Oriented Programming (OOP) is a programming paradigm that helps developers structure code in a more organized and modular way. One of its core features is the class, a blueprint used to create objects that represent real-world entities. Understanding how classes work is essential for building scalable and maintainable software.

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What Is a Class?

A class is a user-defined blueprint that describes the structure and behavior of an object.
It defines:

• Attributes → the data or characteristics of the object
• Methods → the actions or behaviors the object can perform

You can think of a class like a template for making multiple identical objects, each containing its own data but sharing the same structure.

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Why Are Classes Useful?

Classes help solve programming problems in a structured way by:

1. Modeling real-world entities
   For example, a bank account, a student, or a car.

2. Grouping related data and functions together
   This makes the program cleaner and easier to understand.

3. Reusing code
   Once a class is created, you can make as many objects from it as needed.

4. Encapsulating data
   Classes keep related operations together, making it harder to accidentally misuse data.

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Attributes and Methods

Attributes

Attributes are variables contained inside a class.
They store information about the object.

Example attributes in a bank account:

• account_number
• owner
• balance

Methods

Methods are functions defined inside a class.
They define the behaviors that the objects created from the class can perform.

Example methods:

• deposit()
• withdraw()
• check_balance()

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Example: A Simple BankAccount Class

Below is an easy implementation of a BankAccount class in Python:

class BankAccount:
    def __init__(self, account_number, owner, balance=0):
        self.account_number = account_number
        self.owner = owner
        self.balance = balance

    def deposit(self, amount):
        self.balance += amount
        return f"Deposited {amount}. New balance is {self.balance}."

    def withdraw(self, amount):
        if amount > self.balance:
            return "Insufficient funds."
        self.balance -= amount
        return f"Withdrew {amount}. New balance is {self.balance}."

    def check_balance(self):
        return f"Account Balance: {self.balance}"

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How the Class Works

1. The __init__ Method

This special method initializes a new object.
It sets the starting values for the attributes:

self.account_number = account_number
self.owner = owner
self.balance = balance

Every object created from this class will store these values independently.

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2. Operations Through Methods

Deposit

Adds money to the balance.

Withdraw

Checks if the account has enough funds before withdrawing.

Check Balance

Returns the current balance.

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Creating an Object From the Class

Here is how you can create a BankAccount object and perform actions:

# Create a new bank account
account1 = BankAccount("ACC123", "John Doe", 500)

# Deposit money
print(account1.deposit(300))

# Withdraw money
print(account1.withdraw(200))

# Check balance
print(account1.check_balance())

Output example

Deposited 300. New balance is 800.
Withdrew 200. New balance is 600.
Account Balance: 600

Each method changes or accesses the data stored in the object.

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Classes allow you to:

• Structure code based on real-world concepts
• Keep data and behavior packaged together
• Build programs that are easier to expand and maintain

In real applications, the BankAccount class could be expanded with security checks, transaction histories, or links to user profiles. This demonstrates how classes form the foundation of more complex systems.