What are the eight basic data types of Java?

The eight basic data types of Java are: 1. Integer type byte, short, int, long; 2. Character type char; 3. Floating point type float, double; 4. Boolean type boolean.

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Since the release of Java, the basic data types have been in the Java language Part of them are byte, short, int, long, char, float, double, boolean.

##where:

Integer type: byte, short, int, long

Character type: char

Floating point type: float, double

Boolean type: boolean

1. Integer type

Integer data in Java are signed numbers, that is, the first bit is 0, which means a positive integer. A bit of 1 represents a negative integer. In computers, negative numbers are represented by complements, so how are complements calculated?

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Complement code = negate the source code by 1;

For example:

22, represented in the computer as 00010110,

-22, negated: 11101001, plus 1: 11101010

byte

byte is an integer type in Java. The length is 1 byte and 8 bits. The value is 10000000 (-128) to 01111111 (127). The default value of variable initialization is 0. Packaging Class Byte

short

#short is an integer type in Java, with a length of 2 bytes and 16 bits, and a value of 10000000 00000000 (-32768) To 01111111 11111111 (32767), the default value of variable initialization is 0, and the packaging class Short

int

int belongs to the integer type in Java, The length is 4 bytes and 32 bits, and the value is -2^31 (-2,147,483,648) to 2^31-1 (2,147,483,647). The default value of variable initialization is 0, packaging class Integer

long

long is an integer type in Java, with a length of 8 bytes and 64 bits, and a value of -2^63 (-9,223,372,036,854,775,808) to 2^63-1 (9,223,372,036,854,775,8087). The default value of variable initialization is 0 or 0L, and the packaging class Long

2. Floating point type

Floating point data in Java cannot be converted into binary Direct representation, but an approximate data representation for real numbers, which follows the IEEE 754 standard

float

float belongs to Java Floating point type, also called single-precision floating point type, length is 4 bytes and 32 bits, variable initialization default value is 0.0f, packaging class Float

1. float structure

Contains three parts:

Sign bit, exponent bit, mantissa bit

##Length1bit8bit23bitExplanation0 represents a positive number, 1 represents a negative numberThe format is ,

2. Float value

Formal form:

Informal form:

It is easy according to the above formula The calculated value range of float is:

(minimum value, when the sign bit S is 1 and the exponent bit E is 255)

(Maximum value, when the sign bit S is 0 and the exponent bit E is 255)

can get the approximate data in between.

Note: Depending on the different values ​​of the exponent bit and the mantissa bit, there are many special cases, such as NAN, positive infinity, and negative infinity, but they are basically not used in daily life, so we will not go into details here; At the same time, because it is an approximate value, the amount cannot be expressed. It is recommended to use BigDecimal

double

double is a floating point in Java. type, also called double-precision floating-point type, with a length of 8 bytes and 64 bits. The default variable initialization value is 0.0d. The packaging class Double

1. The double structure

contains Three parts: Sign bit, exponent bit, mantissa bit

##Sign bit (S)	Exponent bit (E)	Mantissa bit(M)
	, E Value range: (0,255), exponent value: (	is in the form of 1.M or 0.M. Among them, when E=0, take 1.M, which is called the normal form. When E! = 0, take 0.M, which is called the informal form

##Sign bit (S)Exponent bit (E)Mantissa bit(M)##LengthExplanation, E value range : (0,2047), the exponent bit value: (2. Double value

1bit	11bit	52bit
0 represents a positive number, 1 represents a negative number	The format is	, ) is in the form of 1.M or 0.M. Among them, when E=0, take 1.M, which is called the normal form. When E! = 0, take 0.M, which is called the informal form

Formal form:

Informal form:

According to the above formula, it is easy to calculate the value range of double:

(minimum value, when the sign bit S is 1. The exponent bit E is 2047)

(maximum value, when the sign bit S is 0, the exponent bit E is 2047)
can get the approximate data in between.

Note: Depending on the different values ​​of the exponent bit and the mantissa bit, there are many special cases, such as NAN, positive infinity, and negative infinity, but they are basically not used in daily life, so we will not go into details here; At the same time, because it is an approximate value, the amount cannot be expressed. It is recommended to use BigDecimal

## to express the amount. Three. Character type

char

Char is a character type in Java, occupies 2 bytes and 16 bits. It can assign single characters and integer values. There is no default value for variable initialization, and it is a packaging class Character.

For example:

char a = 'a';

char a = '中';

char a = 12; // Value range 0~65536, because the char type has corresponding values ​​in ASCII character encoding, and can be directly operated and output the corresponding characters in the character table

4. Boolean type

boolean

The JVM does not provide boolean-specific bytecode instructions, and boolean type data is passed through After compilation, it will be represented by the int type in the JVM. At this time, the boolean data is 4 bytes and 32 bits, and the boolean array will be encoded into a byte array of the Java virtual machine. At this time, each boolean data occupies 8 bits per byte.

--Java Virtual Machine Specification

There are only two values ​​true, false, and the default value of variable initialization is false

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