Data types in Java are divided into eight categories, 7 basic data types, and a reference type. The 
computer uses the two-level original code's complement to represent the number of symbols, that is, 1B (byte, byte) = 8 bit,
so just Have
byte 1 byte is eight bits maximum 127 minimum -128
1. Why is 8-bit not 255 but 127?
Answer: The highest bit of the number of signs is the service number. Bit 0 means positive number 1 means negative number
2. We all know that the range of numbers that a Byte can express is [-128,127], so how does -128 come from?
Answer:
Positive number:
original code== inverse code== complement code
ie: original: 0000 0001 ----- reverse: 0000 0001 ------ complement: 0000 0001
negative number:
Inverse code == the non-sign bit of the original code is inverted
Complement code == Inverse code +1
That is, the original: 1000 0001 ------ reverse: 1111 1110 ------ supplement: 1111 1111
The original code, the complement code, and the complement code can all represent the same number. The
computer uses the complement code to store a number.
So the number corresponding to the data type is easy to remember
byte: The
byte data type is 8-bit , signed, and an integer represented by two's complement; the
minimum value is -128 (-2^7); the
maximum value is 127 (2^7-1);
short：
The short data type is a 16-bit , signed integer expressed in twos complement. The
minimum value is -32768 (-2^15); the
maximum value is 32767 (2^15-1);
int：
The int data type is a 32-bit signed integer expressed in twos complement; the
minimum value is -2,147,483,648 (-2^31); the
maximum value is 2,147,483,647 (2^31-1);
long：
The long data type is a 64-bit signed integer represented by twos complement; the
minimum value is -9,223,372,036,854,775,808 (-2^63); the
maximum value is 9,223,372,036,854,775,807 (2^63 -1);
float：
The float data type is a single-precision, 32-bit , floating-point number conforming to the IEEE 754 standard;
float can save memory space when storing large floating-point arrays;
double：
The double data type is a double-precision, 64-bit , floating-point number conforming to the IEEE 754 standard;
Question : Why is the same 32-bit 64-bit double, float larger than int...
Answer : float is not simply stored like 101010, it divides 4 bytes into
sign bit, exponent bit, mantissa bit such as 1.123123*10^35;
3 parts are fixed, because there are exponents, the storage range is of course larger than int Big. The larger the value, the less precise
boolean：
The boolean data type represents one bit of information;
there are only two values: true and false;
char：
The char type is a single 16-bit Unicode character ; the
minimum value is \u0000 (ie 0); the
maximum value is \uffff (ie 65,535); the
char data type can store any character;
C++7 basic data types
Type keyword placeholder
Boolean bool 1 bit
Character char 1 byte
Integer int 4 bytes
Floating point float 4 bytes
Double floating point double 8 bytes
Untyped void
wide character Type wchar_t 2 or 4 bytes
The data type modifier
signed has a sign bit (in fact, the default type is this so it can be omitted) signed
unsigned unsigned (1 byte 8-bit binary highest bit is the sign bit and the sign bit is removed) For example: the value range of char is -127 to 128, the sign bit is removed, the value range of unsigned char is 0 to 255
short shortened byte short int 2 bytes
long increased byte long int 8 bytes