# OOP
Def: 一種軟體的設計方式,其概念為 object
* what is object ?
* 廣義: OOP 裡面所有東西都是 object
* 狹義: Data + Behavior = Object (ie Object is a virtual entity with specific list of properties which can distinguish it from other objects and behavior which allow to manipulate with these properties)
* class 的實例即為 object

* what is a class?
* class is a template for objects

OOP 優點:modularity, scalability, lower cost of development, security & reliability

## OOP Principles
### inheritance 繼承
Inheritance allows you to create new class based on another one. New class can extend existing one and share properties and behavior.

好處: 避免重複造輪
名詞解釋: New class 又叫做 child class, basic class 又叫做 parent class
## Encapsulation 封裝
keep data and code that can manipulate this data together.
### 修飾符

* Default:
* Protected
* Public: 可被任意其他類別存取
* Private: 只能在該類別內部存取,不能被其他類別存取
## Polymorphism
One interface and multiple implementations. (method overwriting)
## Abstraction
對特定案例若抽象的好,就可以避免重複的code

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## 1-1 Classes and Object
class 組成包含: constructor, fields, methods, initialization blocks, nested classes

### Class 的 Property: Field
儲存 class 的狀態或是屬性。在 class 中宣告 Field 可以有不同的 modifier

## initialization blocks
分為 static and non static

使用時機:有些 fields 想在初始化帶上預設值

static block initialization 範例: driver class