composition

Composition in OOP

Suppose a BankAccount must have a Customer.
That Customer is created inside the BankAccount — not shared with anyone else.

If the account is deleted, the customer details are also gone.

That’s Composition.

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Composition means:

• One class owns the other class object

• The lifecycle of the owned class depends on the owner

• Strong bonding → like “part-of” relationship

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In simple English:

• Aggregation → "Has-a" (loose)

• Composition → "Part-of" (tight)

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Simple Code:

Copyclass Customer:
    def __init__(self, name, cnic):
        self.name = name
        self.cnic = cnic

class BankAccount:
    def __init__(self, name, cnic, balance):
        self.customer = Customer(name, cnic)  # Composition: created inside
        self.balance = balance

    def show_details(self):
        print(f"{self.customer.name} has balance {self.balance}")

How to Use:

Copyacc = BankAccount("Maham", "12345-6789012-3", 5000)
acc.show_details()

Output:

CopyMaham has balance 5000

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Key Points:

• Customer object is part of BankAccount

• If BankAccount is deleted → Customer is deleted too

• Customer is not shared with any other account

• It’s a tight relationship

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Analogy:

• BankAccount can’t exist meaningfully without its Customer

• Customer created inside BankAccount → composition