Java Basic 之一

Class(類別) 種類～
public: can be used by anyone (even outside of the package)
(none): can be used within this package
abstract: 代表類別內有尚未實做的method
final: 代表此類別不能被別人 inherit

method 範圍種類～
public: can be accessed by anyone (even outside of the package)
protected: can be accessed within this package, **[also... subclass can accessed it even not in the same package]**
(none): can be accessed within this package.
private: can be accessed only by this class.
method 特性種類～
static: 靜態method, 不用被new就可使用
final: 不能被subclass override.
abstract: 只有宣告沒有實體程式的method, child class可以自己寫程式碼.
native: 代表method是用別的程式語言寫成的 (非JAVA)
synchronized: 此method有multi-threads的共用資料, 需被“Monitor” 機制控管.

variable 種類～
static: 靜態變數 (can be used as Class.XXX)
final: 不能改變的值
transient: 暫存變數 (在Object Serialization時, 此變數不存入Hard Drive)
volatile: 迅變變數 (宣告此變數為多工處理的共用變數。Java VM 會保證 volatile 變數安全地被各 client program 存取)

Overloading～
一個Class(類別)擁有一個以上的同名method(函式)，稱為 overloading.
ex:
class Rectangle{
int l, b;
float p, q;
public Rectangle(int x, int y){
l = x;
b = y;
}
public int first(){
return(l * b);
}
public Rectangle(int x){
l = x;
b = x;
}
public int second(){
return(l * b);
}
public Rectangle(float x){
p = x;
q = x;
}
public float third(){
return(p * q);
}


}

Overriding～