Java變數型態,溢位overflow,補數

w3schools陳述Java定義變數的規則

變數名稱的規定： 使用字母,數字,底線_和金額符號$命名 必須使用字母或金額符號$開頭或底線_開頭 必須使用小寫字母開頭，不能使用空白 也可以使用金額符號$開頭或底線開頭，但w3schools的示範案例不會如此做 字母有大小寫之分，例如"myVar"和"myvar"是不同的變數 不能使用保留字當作變數名稱，例如int或boolean等

The general rules for naming variables are: Names can contain letters, digits, underscores, and dollar signs Names must begin with a letter Names should start with a lowercase letter and it cannot contain whitespace Names can also begin with $ and _ (but we will not use it in this tutorial) Names are case sensitive ("myVar" and "myvar" are different variables) Reserved words (like Java keywords, such as int or boolean) cannot be used as names

來源: https://www.w3schools.com/java/java_variables_identifiers.asp

Data Type	Size	Description	
byte	1 byte	Stores whole numbers from -128 to 127	
short	2 bytes	Stores whole numbers from -32,768 to 32,767	
int	4 bytes	Stores whole numbers from -2,147,483,648 to 2,147,483,647	
long	8 bytes	Stores whole numbers from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807	
float	4 bytes	Stores fractional numbers. Sufficient for storing 6 to 7 decimal digits	
double	8 bytes	Stores fractional numbers. Sufficient for storing 15 decimal digits	
boolean	1 bit	Stores true or false values	
char	2 bytes	Stores a single character/letter or ASCII values

資料型態	長度(位元組)	範圍最小	範圍最大
位元數	1位元組=8位元	-128	127
短整數	2位元組=16位元	-32,768	32,767
整數	4位元組=32位元	-2,147,483,648	2,147,483,647
長整數	8位元組=64位元	-9,223,372,036,854,780,000	9,223,372,036,854,780,000
浮點數	4位元組=32位元	1.4*10^-45	3.4*10^38
倍精數	8位元組=64位元	4.9*10^-324	3.4*10^308
布林	1位元	false	true
字元	2位元組=16位元	'\u0000'	'\uffff'

public class Main {
  public static void main(String[] args) {
    float f1 = 35e3f;
    double d1 = 12E4d;
    System.out.println(f1);
    System.out.println(d1);  
    System.out.println( Byte.MIN_VALUE ); 
    System.out.println( Byte.MAX_VALUE ); 
    System.out.println( Short.MIN_VALUE ); 
    System.out.println( Short.MAX_VALUE ); 
    System.out.println( Integer.MIN_VALUE ); 
    System.out.println( Integer.MAX_VALUE ); 
    System.out.println( Float.MIN_VALUE );
    System.out.println( Float.MAX_VALUE ); 
    System.out.println( Double.MIN_VALUE ); 
    System.out.println( Double.MAX_VALUE );
    System.out.println( Integer.toString( Character.MIN_VALUE ) ); 
    System.out.println( Integer.toString( Character.MAX_VALUE ) );
  }
}

public class Main {
  public static void main(String[] args) {
    char s = 40845;     //宣告字元 s 16進位'\u9f8d'表示 
    System.out.println(s);
    System.out.println(s % 128);
    System.out.println(s % 128 -128);
    System.out.println(s % 32768);
    System.out.println(s % 32768 -32768);
    System.out.println( (byte) s);  
    System.out.println( (short) s);  
    System.out.println( (int) s);  
    System.out.println( (long) s);  
  }
}