Polymorphism

物件導向程式設計 object-oriented-programming (OOP)

物件導向程式設計 object-oriented-programming (OOP) 是一種程式語言模型 (programming language model),程式需要圍繞著物件而不是圍繞著 function 和邏輯。

Object-oriented programming (OOP) is a programming language model in which programs are organized around data, or objects, rather than functions and logic. An object can be defined as a data field that has unique attributes and behavior.

當你看到 class 跟 object 可以把它們看成是相同的東西,因為英文通常會寫成一類物件 (a class of objects)

物件裡面可以包含兩個東西:

  • 唯一的屬性 unique attributes
  • 操作屬性的行為 behavior that manipulate it

物件導向裡面,行為又可以稱作為方法 method

定義

物件導向有四個基本的原則,分別是:

封裝 Encapsulation

封裝是一個物件導向的概念,它將屬性 (data) 和操作屬性的行為 (function) 綁在一起,同時避免外部的干擾和誤用。data hiding 能夠把不需要透露給外部的資料隱藏起來,讓外部無法存取。

Encapsulation is an Object Oriented Programming concept that binds together the data and functions that manipulate the data, and that keeps both safe from outside interference and misuse.

抽象 Abstraction

抽象是一種設計 programming 的技術,需要將介面 (interface)實作 (implementation) 的分離。簡單來說就是設計 API 的介面。在 C++ 需要把設計好的介面放在 public 底下。

Abstraction is a programming (and design) technique that relies on the separation of interface and implementation.

繼承 Inheritance

在定義物件時,子類 (subclass) 可以繼承一個或多個物件 classes。

Inheritance is the concept that when a class of objects is defined, any subclass that is defined can inherit the definitions of one or more general classes

多型 Polymorphism

在物件被繼承的時候,允許變數、函數或物件具有多於一種形式。相關的概念有 dynamic binding,在 C++ 裡面需要用到 virtual

Polymorphism is the characteristic of being able to assign a different meaning or usage to something in different contexts - specitically, to allow an entity such as a variable, a function or, an object to have more than one form.

比較 Encapsulation vs Abstraction

看完定義以後,會不會覺得封裝 (Encapsulation) 跟抽象 (Abstraction) 的定義有點類似:

  • 封裝強調的是綑綁 data 的機制,和使用這些 data 的 function

Data encapsulation is a mechanism of bundling the data, and the functions that use them

  • 抽象強調的是暴露介面和隱藏實作細節的機制

Data abstraction is a mechanism of exposing only the interfaces and hiding the implementation details from the user.

Example Code

以下是程式碼範例:

Reference