corejavae10v1p3.3 3rd Java BASIC Programming Structure-3.3 data types

3.3 Data types

The data type mentioned here refers to the basic data type in Java 8, which is the original existence.

Method of literal representation of different binary numbers

In-process	Literal representation method	Example	Whether the default	JDK Version Support
2 binary	0b or 0 B prefix (every 4 bits available _ delimited)	0b1001,0b1111_0100_0010		Java SE 7 Start
8 binary	0 prefixes	010
10 binary		010	√
16 binary	0x or 0X prefixes	0xCAFE

No number of unsigned types in Java

It makes no sense to talk about default values in Java, where the default value of a data exists only when it is declared as a member variable or as a static variable and initialized, and a compiler error occurs when a variable is not initialized.

3.3.1 Integer type (4 kinds)

td> 

type	bytes	indicates range	default	approximate range	literal representation method /td>	Example	is the default literal type	recommended
byte	1	–128 to 127	0	[
short	2	–32,768 to 32,767	0	30,000	&NB SP;
int	4	–2,147,483,648 to 2,147,483, 647	0	2 billion		√	√
long	8	– 9, 223,372,036,854,775,808 to 9,223,372,036,854,775,807	0L	9*1018	l or L suffix (400L)	400l< /td>

3.3.2 Floating point type (2 kinds)

Type	Number of bytes	Representation Range	Default value	Valid digits (accuracy) (10 binary)	Literal representation method	Example	Is the default literal type	Is it recommended to use
Float	4	±3.40282347e+38f	0.0f	6-7 Guests	F or F suffix	3.14F
Double	8	±1.79769313486231570e+308	0.0d	15 Guests	D or D suffix	3.14d,3.14	√	√

16 binary exponential floating-point numeric representation method

Base	Representation method	Example	General presentation Methods
With 2 as the base	0x***p*** Mark (Mantissa with 16-in, exponent with 10-binary)	0x1.0p-3	1.0x2-3

3 Special floating-point numbers

Double.positive_infinity	Positive Infinity
Double.negative_infinity	Negative infinity
Double.NaN	Non-number (0/0 or negative square root)

The 1.Double class is an object wrapper over the Double type, java.lang.Double

System.out.println (2.0-1.1)

The output is 0.8999999999999999 instead of 0.9, the floating-point number in the actual storage with 2 binary storage, there is a loss of precision, a stake in the numerical calculation can not have any rounding error, using the BigDecimal class

3.3.3 character type (1 kinds)

The char characters in Java represent Unicode (that is, UTF-16) encoded characters.

Type	Number of bytes	Representation Range	Default value	Representation method	Example
Char	2	\u0000 to \uffff	' \u0000 '	' tags, which can be translated using \u and special characters	' A ', ' \u2122 ', ' \ n '

Commonly used char characters and translation characters

form of translation	Name	Unicode value
\ n	Line break	\u000a
\ r	Enter	\u000d
\ t	Tab	\u0009
\"	“	\u0022
\‘	‘	\u0027
\\	\	\u005c
	π, the symbol of the digital pi	\u03c0
	?, trademark symbol	\u2122

Unicode-type translatable characters can be used directly in the source code

 Public Static void Main (string\u005b\u005d args)

Equivalent to

 Public Static void Main (string[] args)

3.3.4 Unicode with Char

3.3.5 Boolean type

Type	Default value	Number of bytes	Representation method	Example
Boolean	False	After compilation, the int data type in the JVM is used instead, and the Boolean array is encoded into a byte array of the Java virtual machine, with each element having a Boolean element of 8 bits. This way we can conclude that the Boolean type takes up 4 bytes, and is 1 bytes in the array.	True,false	True,false

Boolean and other types are non-convertible, in C + +, 0 means false, and non-0 means no in True,java.

corejavae10v1p3.3 3rd Java BASIC Programming Structure-3.3 data types