What are the data types in the database?

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Data types are: 1, integer type [byte, short, int, long]; 2, floating point type [float, double]; 3, character type char;4, Boolean type boolean.

The data types are:

1) four integer types (byte, short, int, long):

Byte:8 bit, used to represent the smallest unit of data, such as data in a file,-128 to 127

Short:16 bit, rarely used,-32768 ~ 32767

Int:32 bit, most commonly used,-2 ^ 31-1 ~ 2 ^ 31 (2.1 billion)

Long:64 bit, second commonly used

Note: int item5; / 5 is called a direct quantity (or literal quantity), that is, a constant written directly.

The whole numeric area is int by default, so add L or l after the defined long data.

Variables less than 32 digits are calculated according to the int result.

Strong converters take precedence over mathematical operators. See examples in constants and variables.

2) two types of floating point numbers (float, double):

Float:32 bit, suffix F or fjore 1-bit symbol bit, 8-bit index, 23-bit effective Mantissa.

Double:64 bit, most commonly used, suffix D or dline 1 symbol bit, 11-bit index, 52-bit valid tail

Note:

Binary floating point number: 1010100010 "101010001.0" 2 "10101000.10 * 2 ^ 10 (power 2) = 1010100.010 * 2 ^ 11 (power 3) =. 1010100010 * 2 ^ 1010 (to the 10th power)

Mantissa:. 1010100010

Index: 1010

Cardinality: 2

Floating-point numeric float is double by default, so adding F or fumbdouble after the defined float data can not write a suffix, but in decimal calculation, the precision of writing D or X.X doubles is not as high as long, and the significant digits (Mantissa) are short.

The range of float is larger than long index can be very large.

Floating-point numbers are imprecise and cannot be accurately compared.

3) A character type (char):

The char:16 bit, which is an integer type, 1 character (which can be a Chinese character) enclosed in single quotation marks, is represented by a Unicode code, 0 ~ 2 ^ 16-1 (65535).

Note: cannot be 0 characters.

Escape character:\ nnewline\ r carriage return\ t Tab character\ "double quotation marks\\ indicates a\"

Two characters char in the middle with "+" connection, the internal character into the int type, and then add operation, the essence of char is the number! Binary, when displayed, is displayed as characters after "processing".

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

5) Type conversion:

Char-- > automatic conversion: byte-- > short-- > int-- > long-- > float-- > double

Forced conversion: ① loses precision and produces errors, and all digits after the decimal point are discarded. ② is easy to exceed the value range.

6) memory:

8 bits: Byte (byte type)

16 bits: short (short integer), char (character type)

32-bit: int (integer), float (single precision / floating point)

64-bit: long (long integer), double (double precision)

Last one: boolean Boolean type

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