Java chapter II variables, data types, and operator notes

Java chapter II variables, data types, and operators

One , variable: a basic unit that stores data.

Second , the Declaration and assignment of variables:

1) Declare and assign values: Data type variable name = value ; Example:int price=1000;

2) Declaration, assignment is divided into two steps: Data type variable name ; Example: int price;

variable Name = value ; price=1000;

Three , the data type 2 kinds:

1) basic data type 8 kinds:

        Byte  length: - 128~127 ( -2 7 2 7 1 )

2 of the Short-2 , minus 1 in the four-time square .

The Int-2 of the two to 2 minus 1 .

The Long-2 of the Five-to -2 reduction of 1 99l

Float 99f

Doubles Double price=32.5;

Boolean True (true) False (false) bolean isbrand=true

Char one character , two byte range 0~65535 reference ASCII character encoding table Char sex=   ' Male '; char num=65; ( output A)

2) Reference data type:

String strings name=" Zhang San ";

Class

Interface

Four , the variable naming specification:

English words or pinyin

Initials : Starts with letters, underscores, and$ ;

When multiple words are composed of variable names: Named by the Camel, example:studentname

The name of the variable should be the result of knowing the meaning of the name

assignment operator:= assigns the right value to the left

Six , arithmetic operators:+-*/% ( remainder )

Seven ,num++;//num=num+1;num+=1;

Num--;//num=num-1;num-=1;

System.out.println (--num);// calculate and re-output first (++num same )

System.out.println (num--);// Output recalculation First (num++ same )

Eight ,double avg= (90+99)/3.0 Automatic type conversion occurs

the conditions for automatic type conversion ;

1) Type-compatible:(int and double are numeric )

2) The target type is greater than the source type

Ix. Coercion Type conversion: (data type) variable name (data type) value

Example:double num=5.5; int result= (int) num;

or int result= (int) 5.5;

Java chapter II variables, data types, and operator notes