Chang Wei (variables and constants) is easy to understand

Distinguishing statement

Generally will 1,2,3,'a','b',true,false,''helloWorld'' Such as character constants

Use final Embellished PI Is a symbolic constant .

Variable and constant naming specification

* You can't call names blind , You have to see what it means

* Class member variable ： The first letter is lowercase or hump principle ：monthSalary

* local variable ： The first letter is lowercase or hump principle

* Constant ： Capital letters and underscores :MAX_VALUE

* Class name ： The starting letter is capitalized or humped ：Man,GoodMan

* Method name ： Capital letters or hump rules ：run（）,runRun()

public class TestConstant{
    public  static vois main(String[] args){

        final double PI =3.14;

        final int MAX_SPEED = 120;// Constant naming ; All in capital letters , Underline the words 

        int r =4;
        double area = PI*r*r;
        double circle = 2*PI*r; 
        System.oub.println(" The area is :"+area);
        System.out.println(" The circumference is ："+cirxle);  
    }
}