OOP

OOP物件導向

• 所有資料都是物件
• 能夠提高軟體的重用姓,擴充性及維護姓
• Encapsulation 封裝：外部程式碼只要透過統一介面來進行存取即可，而無需瞭解其中的運算過程
• Inheritance 繼承：有父類別(或稱基底類別Base Class)及子類別(Sub Class)的階層關係。子類別會擁有父類別公開的屬性(Attribute)及方法(Method)
• Polymorphism 多型：能夠讓程式碼的相依性不會那麼高，並且透過統一的介面來彈性擴充功能

Class類別

• user-defined data structure that binds the data members and methods into a single unit
• a blueprint or code template for object creation
• 第一個英文字母要大寫
• Class裡面的method第一個參數都要設為self
• Class要取用內部attribute都要加上self.xxx
• __init__函數：當Class被創建的時候會自動被執行1次,初始化的程式碼

class Person:
    def __init__(self, name, sex, profession, study):   //初始化的程式碼
        #States (instance variables)
        self.name = name
        self.sex = sex
        self.profession = profession
        self.study = study

    # Behavior (instance methods)
    def show(self):
        print('Name:',self.name,'Sex:',self.sex,'Profession:',self.profession) 
    def work(self):
        print(self.name,' works as a ',self.profession)
    def study(self):
        print(self.name,' studies ',self.study,' hours per week')

# create instance of a class object
jessa = Person('Jessa', 'Female', 'Engineer',10)
# call methods
jessa.show()
jessa.work()
jessa.study()

Encapsulation封裝

• 外部程式碼只要透過統一介面來進行存取即可，而無需瞭解其中的運算過程
• 類別裡的attribute及method私有化

# Creating a class
class MyClass(): 
    def __init__(self,fname,pwd=999):
        self.fname = fname                  //can be accessed from the outside
        self.__pwd = pwd                    //cannot be accessed from the outside
    # Declaring public method               
    def fun(self):                          //can be called outside of this class
        print("This is a Public method")
    # Declaring private method
    def __fun(self):                        //cannot be called outside of this class
        print("This is a Private method")

x = MyClass('james')//create an instance of class
x.fname             //can access fname
x.__pwd             //cannot access this attribute. give error
x.fun               //calling public method
x.__fun             //calling private method will give error

######################################################################################
class Bank():
    def __init__(self,uname):
        self.__name = uname             //內部attribute
        self.__balance = 0              //內部attribute
    def save(self, amt):                //只能在method中操作到內部attribute
        self.__balance += amt 
        print("存款:",amt,"完成") 
    def withdraw(self,amt):
        self.__balance -= amt           //只能在method中操作到內部attribute
        print("提款:",amt,"完成") 
    def balance(self):
        print("餘額:",self.__balance)   //只能在method中操作到內部attribute

mybank = Bank('weili')
mybank.save(100)
mybank.withdraw(25)
mybank.balance()

Inheritance繼承

• 有父類別(或稱基底類別Base Class)及子類別(Sub Class)的階層關係
• 子類別會擁有父類別所有屬性(Attribute)及方法(Method)

# Creating a Base class
class Base:
     # Declaring public method
    def fun(self):
        print("Public method")
     # Declaring private method
    def __fun(self):
        print("Private method")
 
# Creating a derived class
class Derived(Base):
    def __init__(self):
        # Calling constructor of Base class
        Base.__init__(self)
 
    def call_public(self):
        # Calling public method of base class
        print("\nInside derived class")
        self.fun()
 
    def call_private(self):
        # Calling private method of base class
        self.__fun()

Polymorphism多型

• 能夠讓程式碼的相依性不會那麼高，並且透過統一的介面來彈性擴充功能
• 當子類別與父類別有同一個名稱的method時,子類別會父寫父類別的method

class Car:
    def __init__(self, name, color, price):
        self.name = name
        self.color = color
        self.price = price
    def show(self):
        print('Details:', self.name, self.color, self.price)
    def max_speed(self):
        print('Car max speed is 150')
    def change_gear(self):
        print('Car change 6 gear')

# inherit from Car class
class SportsCar(Car):
    def max_speed(self):                        //child can rewrite method 
        print('Sports Car max speed is 240')
    def change_gear(self):                      //child can rewrite method
        print('Sports Car change 7 gear')

c1 = SportsCar('Audi999', 'white', 75000)
c1.show()
c1.max_speed()
c1.change_gear()