Since the release of Java basic data type is part of the Java language, namely *** byte, short, int, long, char, float, double, boolean ***.
among them:
Int: byte, short, int, long
Character: char
Float: float, double
Boolean: boolean
Prior to the detailed description, to what science, Java smallest calculation unit *** *** bytes, 1 byte = 8 bits (bit).
A. Integer
In Java integer number of data symbols belong to, i.e. the first bit to 0 indicates a positive integer, the first bit to 1 indicates a negative integer. A negative number is represented by a complement in the computer, then complement how to calculate it?
Complement source negated = + 1;
Such as:
22, in the computer that is 00,010,110,
-22 negated: 11101001, plus 1: 11,101,010
byte
Java byte in the integer part of a length of 1 byte 8bit, value 10000000 (-128) to 01111111 (127), the default value is variable is initialized to 0, Byte packaging
short
the integer part of the Java short length of 2 bytes 16bit, 1,000,000,000,000,000 value (-32768) to 0,111,111,111,111,111 (32767), the default value is variable is initialized to 0, packaging Short
int
the integer part of the Java int length of 4 bytes 32bit, the value -2 ^ 31 (2,147,483,648) to 2 ^ 31-1 (2,147,483,647), the default value is variable is initialized to 0, packaging Integer
long
the integer part of the Java long, 8 bytes in length 64bit, the value -2 ^ 63 (-9,223,372,036,854,775,808) to 2 ^ 63-1 (9,223,372,036,854,775,8087), or the variable is initialized to the default value 0 0L, packaging Long
II. Float
In Java floating-point data can not be directly represented by a binary, but rather a real number for an approximate representation of the data that follows the IEEE 754 standard
float
float part of the Java floating point type, also known as single-precision floating-point, a length of 4 bytes 32bit, variable initialization Default 0.0f, packaging Float
1. float structure
Consists of three parts: a sign bit, the exponent bits, bit mantissa
| Sign bit (S) | Exponent (E) | Mantissa bits (M) | |
|---|---|---|---|
| length | 1bit | 8bit | 23bit |
| Explanation | 0 for positive, 1 for negative | Format  , E value ranges: (0,255),  :( exponent value  , ) |
In the form of 1.M or 0.M. Wherein when E = 0, take 1.M, called normal form, when E! = 0, take 0.M, referred to as non-formal |
2. float value
Normal form:
Informal forms:
Float easily computed according to the above formula in the range of:
(Minimum, take 1 when the sign bit S, exponent bit taken E 255)
(The maximum value, set to 0 when the sign bit S, exponent bit taken E 255)
You can take the approximate data therebetween.
Note: Depending on the value of the exponent bit and mantissa bits, there are many special cases, such as NAN, positive infinity, negative infinity, but usually will not use basic, no depth here; at the same time because it is an approximation, so the amount can not be represented indicating the amount recommended BigDecimal
double
double-type part of the Java floating point, double precision floating point is also called a length of 8 bytes 64bit, variable initialization Default 0.0d, packaging Double
1. double structure
Consists of three parts: a sign bit, the exponent bits, bit mantissa
| Sign bit (S) | Exponent (E) | Mantissa bits (M) | |
|---|---|---|---|
| length | 1bit | 11bit | 52bit |
| Explanation | 0 for positive, 1 for negative | Format  , E value ranges: (0,2047), :( exponent value  ,  ) |
In the form of 1.M or 0.M. Wherein when E = 0, take 1.M, called normal form, when E! = 0, take 0.M, referred to as non-formal |
2. double value
Normal form:
Informal forms:
Easily computed double according to the above formula in the range of:
(Minimum, take 1 when the sign bit S, exponent bit taken E 2047)
(The maximum value, set to 0 when the sign bit S, exponent bit taken E 2047)
You can take the approximate data therebetween.
Note: Depending on the value of the exponent bit and mantissa bits, there are many special cases, such as NAN, positive infinity, negative infinity, but usually will not use basic, no depth here; at the same time because it is an approximation, so the amount can not be represented indicating the amount recommended BigDecimal
III. Character
char
char character belonging to the java, 2 bytes 16bit, characters, and can be assigned a single integer value, no default variable initialization, packaging Character.
Such as:
char a = ‘a’;
char a = 'and';
char a = 12; // ranges from 0 to 65536, as char ASCII character encoding type, a corresponding value can be done directly operation, output the corresponding character in the character table
IV. Boolean
boolean
It does not provide a dedicated boolean in the JVM bytecode instructions, and a boolean data after a compiled JVM will be represented by an int, boolean case 4 bytes of data 32, and will be encoded into a boolean array Java virtual machine byte array, in which case each boolean 1 byte of data accounted for 8bit.
-Java virtual machine specification
Only two values, true, false, false variable initialization defaults