Variables and data types

Java It's a strongly typed language . Data must have certain type before calculation

Basic data type ;   byte /short /int /long/( Accounting for 1-4 byte )

float(4 byte , precision 6-7 position )   double(8 byte , precision 15-16 position )

char Character ;  boolean Boolean type ( Judge / whether )

Reference data type ;  class   /interface  / Array

Character set    GB180309 The latest Chinese character set )

Unicode  International character set

Binary to decimal conversion

example ;  1010=0*2^0+  1*2^1+0*2^2+ 1*2^3

octal :015=5*8^0+1*8^1+0*8^3

Type of plastic surgery

A byte convention is 8 position         Range -128~127

One byte is byte type

Java The default writing shape in is int

Declare different types and add    L or F. Such as long 10=10L;

floating-point

1.0 !=1    Floating point has precision

char type

Occupy 2 byte , Can represent characters , english , Chinese characters , Escape character . stay Unicode In the said .

Variable

First of all Use after assignment .

Variable names are made up of letters , Numbers _  $ And the first letter cannot be a number . You can't use system keywords .

It's usually named after hump , See the name and know the meaning .

Local variables can only be used in their scope :

Variables declared in a method can only be used in that method .

Member variables : Variables defined in the class ( It's defined in Outside of the method , Inside of class )

Member variables can be used in all non static methods in a class ;

If there is no initial value ,jvm Default assignment . Such as The default initial value of shaping is 0; Floating point is 0.0 The reference data type is null.

Constant

Initialization is assigned only once , Subsequent operations cannot be modified .

Naming conforms to variable naming rules , When a handful of letters are capitalized , See the words _ Separate .

Arithmetic operator

% Seeking remainder      / to be divisible by        a++ First calculate and then add 1    ++a First plus 1 Re operation .

&& And ( also ):    Short-circuit operation :  The previous operation has false , There's no arithmetic behind it ( If there is a change in the value behind it, it will not be calculated ), Direct output false

!    Take the opposite      !false=true;

An operator    int a=b<<2    Shift binary left 2 position ( Equivalent to times 4)

|| or ( One of them ) ;

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