Java Road Day10 variable

variable

What variables are: that amount may vary

Java is a strongly typed language, each variable must declare its type

Java program variable is the most basic storage unit elements include a variable name, variable type and scope

type varName   [=value] [{,varName[=value]}];

Data type variable name = value; commas may be used to declare the plurality of variables of the same type

Precautions:

• Each variable has a type, type can be a primitive type, it can be a reference type

• Variables must be a valid identifier

• Variable declaration is a complete sentence, so each statement must end with a semicolon

public class Demo3 { public static void main ( String [] args) { / * int A, B, C; can write, but not recommended write int A =. 1, B = 2, C =. 3; * / / * recommendations Thus said focusing readability int. 1 = A; int B = 2; int. 3 C =; * / String name = "Jiang Tao"; char X = 'X'; Double PI = 3.14;    } }
    
        
        
        
        
        
        

        
        
        

Variable Scope

• Class variables

• Instance variables

• Local variables

Demo4 class {public    // class variable static    static Double the salary = 2500;    // Properties: Variable    @ instance variables: subordinate objects; if you do not own initialization, the default value of this type 0.0 0    @ Boolean: the default is to false    // addition to the basic type, the rest of the default values are the null (empty)    String name;    int Age;    // main method    public static void main (String [] args) {      // variables in the process Board , which must be declared and initialized value of        int I = 10;        System.out.println (I);        // variable type variable name Demo4 new new = ();        Demo4 demo4 new new Demo4 = ();        System.out.println ( demo4.age);        System.out.println (demo4.name);


























       System.out.println (the salary); 
       // class variable static 
   }    // other methods    public void the Add () {        System.out.println ();    } }

constant

Constant: can not change the value after initialization! Value will not change.

The so-called constants can be understood as a special kind of variable, after his values ​​are set, not allowed to be changed in the course of running

General constant use uppercase characters

static: Static

final: decisive

Demo5 class {public    // modifier, there is no order    static final double PI = 3.14; // constants can be defined directly referenced    public static void main (String [] args) {        System.out.println (the PI);    } }

* Variable naming conventions

• All variables, methods, classes name: See name EENOW

• Class member variables: the first letter lowercase and hump principles: monthSalary

• Local variables: the first hump principles and lowercase characters

• Constants: uppercase river picture decline line: MAX_VALUE

• Class Name: capitalized and hump principle: Man, Good

• Method name: the first letter lowercase and hump principle: run (), runRun ()

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