學習高校課程-軟體設計模式-OOP 和 UML 類圖 OOP 與 Java（lec1）

Lecture 1：OOP and UML Class DiagramsOOP with Java

OOP 和 UML 類圖 OOP 與 Java

Object-Oriented Programming 物件導向程式設計

Class Hierarchies 類層次結構

Superclass and subclass
超類和子類

Pillars of Object-Oriented Programming 物件導向程式設計的支柱

1. Abstraction
   – Modelling attributes and behaviors of real objects, in specific contexts
   抽象——對真實物件的屬性和行為進行建模，具體來說

2. Encapsulation
   – Hiding parts of an object’s states and behaviors from others, and exposing a limited set of interfaces
   – public, private, and protected
   – Interfaces and abstract classes
   封裝
   — 隱藏物件的部分內容和來自他人的狀態和行為，並公開一組有限的介面
   – 公共、私有和受保護
   – 介面和抽象類

3. Inheritance
   – Main benefit: code reuse
   繼承
   — 主要好處：程式碼重用

4. Polymorphism
   – Performing an action in many forms
   – A mechanism for detecting the real class of an object and call its implementation
   多型性
   多種形式執行一個動作
   一種檢測物件的真實類並呼叫其實現方法的機制

OOP with Java: Declaring Classes and Creating Objects Java 的 OOP：宣告類和建立物件

• Class declaration
  類宣告
  

• Creating objects
  建立物件

  • Declaration, instantiation, initialization
    宣告、例項化、初始化
    
  • The reference returned by the new operator does not have to be assigned to a variable
    new 運算子返回的引用不必分配給變數

OOP with Java: Access Control Java 的 OOP：訪問控制

• At the top level
  在頂層
  – public, or package-private (no explicit modifier)
  公共或包私有（無顯式修飾符）
• At the member level
  在成員級別
  – public, private, protected, or package-private (no explicit modifier)
  public、private、protected 或 package-private（無顯式修飾符）

OOP with Java: Inheritance Java 中的 OOP：繼承

• Classes can be derived from other classes, inheriting fields and methods
  類可以從其他類派生，繼承欄位和方法

• Definitions
  定義
  – Subclass (derived class/extended class/child class)
  – Superclass (base class/parent class)
  – 子類（派生類/擴充套件類/子類）
  – 超類（基類/父類）

• Every class has one and only one direct superclass (single inheritance)
  每個類都有一個且僅有一個直接超類（單繼承）
  – Excepting Object, which has no superclass
  除了Object，它沒有超類

• A subclass inherits all the members (fields, methods, and nested classes) from its superclass
  子類繼承其超類的所有成員（欄位、方法和巢狀類）

OOP with Java: What You Can Do in a Subclass Java 的 OOP：在子類中可以做什麼

Use the inherited members as is, replace them, hide them, or supplement them
按原樣使用繼承的成員、替換它們、隱藏它們或補充它們

• Declare a field in the subclass with the same name as the one in the superclass, thus hiding it (NOT recommended)
  – 在子類中宣告一個與超類中的欄位同名的欄位，從而隱藏它（不推薦）
• Write a new instance method in the subclass that has the same signature as the one in the superclass, thus overriding it
  – 在子類中編寫一個新的例項方法，其簽名與超類中的欄位相同，從而覆蓋它
• Write a new static method in the subclass that has the same signature as the one in the superclass, thus hiding it
  –在子類中編寫一個新的靜態方法，該方法與超類中的靜態方法具有相同的簽名，從而隱藏它
• Write a subclass constructor that invokes the constructor of the superclass
  – 編寫一個呼叫超類建構函式的子類建構函式

How about private members in a superclass?

OOP with Java: Abstract and Final Methods/Classes Java 的 OOP：抽象和最終方法/類

• An abstract class is a class declared abstract: it may or may not include abstract methods
  抽象類是宣告為抽象的類：它可能包含也可能不包含抽象方法
• An abstract method is a method declared without an implementation
  抽象方法是宣告但沒有實現的方法
• Final methods and classes
  最終方法和類
  Methods called from constructors should generally be declared final
  – 從建構函式呼叫的方法通常應宣告為final

OOP with Java: Interfaces Java 的 OOP：介面

• Interfaces are contracts
  介面是契約
• A reference type, containing only constants, method signatures,default methods, static methods, and nested types
  引用型別，僅包含常量、方法簽名、預設方法、靜態方法和巢狀型別
• Cannot be instantiated
  無法例項化
  – They can only be implemented by classes or extended by other interfaces
  – 它們只能由類實現或由其他介面擴充套件
• Consisting of modifiers, keyword, interface name, a comma-separated list of parent interfaces (if any), and the interface body
  由修飾符、關鍵字、介面名稱、以逗號分隔的父介面列表（如果有）和介面主體組成
• Interface body can contain abstract methods, default methods,and static methods
  介面體可以包含抽象方法、預設方法和靜態方法

OOP with Java: Implementing and Using Interfaces 使用 Java 進行 OOP：實現和使用介面

• Include an implements clause in the class declaration
  在類宣告中包含 implements 子句
  – Your class can implement more than one interface
  – 你的類可以實現多個介面
• If you define a reference variable whose type is an interface,any object you assign to it must be an instance of a class that implements the interface
  如果定義型別為介面的引用變數，則分配給它的任何物件都必須是實現該介面的類的例項

OOP with Java: Abstract Classes vs. Interfaces Java 中的 OOP：抽象類與介面

• Consider using abstract classes when
  考慮使用抽象類
  – You want to share code among several closely related classes
  – 您希望在幾個緊密相關的類之間共享程式碼
  – You expect that classes extending the abstract class have many common methods or fields, or require access modifiers other than public
  – 您希望擴充套件抽象類的類具有許多通用方法或欄位，或者需要除 public 之外的訪問修飾符
  – You want to declare non-static or non-final fields
  — 您想要宣告非靜態或非最終欄位

• Consider using interfaces when
  考慮使用介面
  – You expect that unrelated classes would implement your interface
  – 您希望不相關的類實現您的介面
  – You want to specify the behavior of a particular data type, but not concerned about who implements its behavior
  – 您想要指定特定資料型別的行為，但不關心誰實現其行為
  – You want to take advantage of multiple inheritance
  – 您想要利用多重繼承