Object-Oriented Programming for Edexcel A-Level | 面向对象编程（Edexcel A-Level）

📚 Object-Oriented Programming for Edexcel A-Level | 面向对象编程（Edexcel A-Level）

Object-oriented programming (OOP) is a paradigm that structures code around objects, which encapsulate data and the methods that operate on that data. For Edexcel A-Level Programming, you need to understand core OOP principles, how to apply them in a high-level language such as Python, and how they improve software design through reusability, modularity, and abstraction.

面向对象编程（OOP）是一种以对象为中心组织代码的范式，对象封装了数据及其操作方法。对于Edexcel A-Level编程考试，你需要理解OOP核心原则，如何在像Python这样的高级语言中应用它们，以及它们如何通过可重用性、模块化和抽象来改善软件设计。

1. What Is Object-Oriented Programming? | 什么是面向对象编程？

In procedural programming, you write a list of instructions for the computer to execute. OOP, in contrast, bundles related properties and behaviours into objects. An object is an instance of a class, which serves as a template. This approach mirrors how we categorise real-world entities, making it easier to model complex systems.

在过程式编程中，你编写一系列让计算机执行的指令。相比之下，OOP将相关的属性和行为捆绑成对象。对象是类的实例，类则是模板。这种方法模拟了我们如何对现实世界实体分类，从而更容易建模复杂系统。

OOP is built on four main pillars: encapsulation, inheritance, polymorphism, and abstraction. Mastering these concepts will not only help you in exams but also prepare you for professional software engineering.

OOP建立在四大支柱之上：封装、继承、多态和抽象。掌握这些概念不仅有助于考试，也能为专业软件工程做好准备。

2. Classes and Objects | 类与对象

A class defines the blueprint for objects. It specifies the attributes (data) and methods (functions) that every object of that type will have. You can create many objects (instances) from a single class, each with its own attribute values.

类定义了对象的蓝图。它指定了该类型每个对象将具有的属性（数据）和方法（函数）。你可以从一个类创建许多对象（实例），每个对象都有自己的属性值。

In Python, you define a class using the class keyword. The example below creates a Car class with a constructor and a method:

在Python中，使用 class 关键字定义类。下例创建了一个 Car 类，包含构造函数和一个方法：

class Car:
    def __init__(self, make, model, year):
        self.make = make
        self.model = model
        self.year = year

    def display_info(self):
        return f"{self.year} {self.make} {self.model}"

my_car = Car("Toyota", "Corolla", 2022)
print(my_car.display_info())

The __init__ method initialises each new object. self refers to the specific instance being created. Once instantiated, you can access attributes and methods using dot notation.

__init__ 方法初始化每个新对象。self 指向正在创建的特定实例。实例化后，可以使用点号访问属性和方法。

3. Attributes and Methods | 属性与方法

Attributes store an object’s state. Instance attributes are defined within __init__ using self, meaning each object has its own copy. Class attributes, defined outside __init__ but inside the class, are shared by all instances.

属性存储对象的状态。实例属性在 __init__ 内部通过 self 定义，这意味着每个对象都有自己的副本。类属性在 __init__ 之外、类内部定义，它们由所有实例共享。

Methods are functions defined inside a class. They always take self as the first parameter, giving them access to the instance’s data. You can also define class methods and static methods, but instance methods are the most common in A-Level syllabi.

方法是在类内部定义的函数。它们始终将 self 作为第一个参数，从而可以访问实例的数据。你也可以定义类方法和静态方法，但在A-Level大纲中最常见的是实例方法。

A well-designed class should only expose necessary methods and hide internal data—a concept we call encapsulation.

一个设计良好的类应该只暴露必要的方法，并隐藏内部数据——这个概念被称为封装。

4. Encapsulation | 封装

Encapsulation is the practice of bundling data with the methods that operate on that data and restricting direct access to some of an object’s components. This prevents accidental interference and misuse of internal state.

封装是指将数据与操作这些数据的方法捆绑在一起，并限制对对象某些组件的直接访问。这可以防止意外干扰和滥用内部状态。

In Python, encapsulation is achieved by convention rather than strict access modifiers. A single leading underscore (_attribute) indicates a protected member that should not be accessed directly from outside the class. Use getters and setters (or