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### What data types does Java support

1） Four types of integers (byte、short、int、long)：    byte：8 position , Used to represent the smallest unit of data , Such as the data in the file ,-128~127    short：16 position , Rarely used ,-32768 ~ 32767    int：32 position 、 The most commonly used ,-2^31-1~2^31  （21 Billion ）    long：64 position 、 The second is often used    matters needing attention ：    int i=5; // 5 It's called direct quantity （ Or literally ）, namely Directly written constants .    The default value of the whole number is int type , So in the definition of long Type data followed by L or l.    Less than 32 The variable of the number of digits , Press int It turns out that .    Strong switches take precedence over mathematical operators . See examples in constants and variables .

2） Two types of floating-point numbers (float、double)：    float：32 position , suffix F or f,1 Bit sign bit ,8 Bit index ,23 Bit effective mantissa .    double：64 position , The most commonly used , suffix D or d,1 Bit sign bit ,11 Bit index ,52 Bit significant tail    matters needing attention ：    Two Into the system floating spot Count ： 1010100010=101010001.0*2=10101000.10*2^10（2 Power )=1010100.010*2^11(3 Power )= . 1010100010*2^1010(10 Power )    mantissa ：  . 1010100010   Index ：1010   base ：2    By default, all floating-point values are double type , So in the definition of float Type data followed by F or f;double Type can not write suffix , But in the calculation of decimals, be sure to write D or X.X    float  It's not as accurate as long high , Effective digits （ mantissa ） short .    float  The range is greater than long  The index can be big .    Floating point numbers are imprecise , You can't compare floating-point numbers exactly .

3） A character type (char)：    char：16 position , It's an integer type , Enclosed in single quotation marks 1 Characters （ It can be a Chinese character ）, Use Unicode The code represents the character ,0~2^16-1（65535） .    matters needing attention ：    Not for 0 Characters .    Escape character ：\n  Line break   \r  enter   \t Tab character   \" Double quotes   \\ It means a \    Two character char Intermediate use “+” Connect , Inside, the characters are converted into int type , And then add ,char The essence is number ！ The binary , On display , after “ Handle ” Display as characters .

4） A boolean type (boolean)：true really   and false false .

5） Type conversion ：       char-->    Automatic conversion ：byte-->short-->int-->long-->float-->double                   Coercive transformation ：① Loss of accuracy , Produce errors , All numbers after the decimal point are discarded .② It is easy to exceed the value range .

6） memory ：8 position ：Byte（ Byte type ）          16 position ：short（ Short ）、char（ Character ）          32 position ：int（ integer ）、float（ Single precision type / floating-point ）          64 position ：long（ Long integer ）、double（ Double precision type ）          the last one ：boolean( Boolean type ）

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