Variables and data types

Variable

Identifiers are generally composed of numbers 、 Letter 、 Underline 、$ Other components , The number can't start ;

Variable input ： First step ：new One Scanner object , for example Scanner sc=new Scanner(System.in); The second step ： Read the string through this object and put it into the variable , for example String name=sc.next();

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data type

Note on conversion between base numbers ：

The way to convert negative decimal to binary ： First convert the absolute value of decimal to binary , Then reverse by bit and add 1;

Negative numbers need complement ： According to the not , add 1;

The way negative binary is converted to decimal ： Subtract binary by one and negate by bits , Then convert to decimal , Add a minus sign at the end ;

A single byte represents an octet binary , Indicates that the integer range is -128~127;

Integer defaults to int type , The floating point type defaults to double type ;

float Type has only seven significant digits ,double A type can represent 15 Significant digits ; And the floating-point type has error in calculation ;

char The type corresponds to ASCII Code value ：'0':48 'A':65 'a':97 Space :32 Line break :10;