カプセル化

カプセル化

カプセル化とは

アクセス修飾子

Public属性とメソッド

# Defines the Person class with public attributes and methods
class Person:
    def __init__(self, name, age):
        self.name = name  # Public attribute
        self.age = age    # Public attribute

    def greet(self):
        print("Hello, my name is " + self.name + "!")  # Public method

# Creates an object of the Person class
person1 = Person("Alice", 30)

# Accesses public attributes and methods
print(person1.name)  # Output: Alice
person1.greet()      # Output: Hello, my name is Alice!

Protected属性とメソッド

# Defines the Employee class with protected attributes and methods
class Employee:
    def __init__(self, name, salary):
        self._name = name      # Protected attribute
        self._salary = salary  # Protected attribute

    def _increase_salary(self, amount):
        self._salary += amount  # Protected method
        print(self._name + "'s new salary is " + str(self._salary))

# Creates an object of the Employee class
employee1 = Employee("Bob", 50000)

# Accesses protected attributes and methods (not recommended)
print(employee1._name)  # Output: Bob
employee1._increase_salary(5000)  # Output: Bob's new salary is 55000

Private属性とメソッド

# Defines the BankAccount class with private attributes and methods
class BankAccount:
    def __init__(self, owner, balance):
        self.__owner = owner    # Private attribute
        self.__balance = balance  # Private attribute

    def deposit(self, amount):
        self.__balance += amount  # Modifies private attribute
        print("Deposited:", amount)
        self.__show_balance()

    def __show_balance(self):
        print("Current Balance:", self.__balance)  # Private method

# Creates an object of the BankAccount class
account1 = BankAccount("Charlie", 1000)

# Attempts to access private attributes and methods (will cause errors)
# print(account1.__owner)        # AttributeError
# account1.__show_balance()      # AttributeError

# Uses public methods to interact with private attributes
account1.deposit(500)  # Output:
                        # Deposited: 500
                        # Current Balance: 1500

カプセル化を使う理由

カプセル化の例：Carクラス

# Defines the Car class with encapsulated attributes and methods
class Car:
    def __init__(self, make, model, year):
        self.make = make          # Public attribute
        self.model = model        # Public attribute
        self.__year = year        # Private attribute

    def get_year(self):
        return self.__year  # Public method to access private attribute

    def set_year(self, year):
        if year > 0:
            self.__year = year  # Public method to modify private attribute
            print("Year updated to", self.__year)
        else:
            print("Invalid year!")

    def __display_info(self):
        print(self.make, self.model, self.__year)  # Private method

    def show_info(self):
        self.__display_info()  # Public method that calls a private method

# Creates an object of the Car class
car1 = Car("Tesla", "Model S", 2020)

# Accesses public attributes and methods
print(car1.make)        # Output: Tesla
print(car1.get_year())  # Output: 2020

# Modifies the private attribute using a public method
car1.set_year(2021)     # Output: Year updated to 2021

# Calls a public method that interacts with a private method
car1.show_info()        # Output: Tesla Model S 2021

# Attempts to access private attributes and methods directly (will cause errors)
# print(car1.__year)         # AttributeError
# car1.__display_info()      # AttributeError

# Defines the Student class with encapsulated attributes
class Student:
    def __init__(self, name, grade):
        self.name = name      # Public attribute
        self.__grade = grade  # Private attribute

    def get_grade(self):
        return self.__grade  # Public method to access private attribute

    def set_grade(self, grade):
        if 0 <= grade <= 100:
            self.__grade = grade  # Updates the grade
        else:
            print("Invalid grade!")

# Creates an object of the Student class
student1 = Student("Diana", 85)

# Accesses and modifies the grade using public methods
print(student1.get_grade())  # Output: 85
student1.set_grade(90)
print(student1.get_grade())  # Output: 90

# Attempts to access the private attribute directly (will cause an error)
# print(student1.__grade)     # AttributeError

よくできました！