java_ variables and constants

A variable (the amount can be altered)

       1. Naming:

                       . A follow identifier naming rules:

                          1. Keyword can not be used as an identifier

                          2. case sensitive

                          3. may contain numbers, letters, underscores, dollar sign $, but not as the beginning of the digital

                       b. Try to use meaningful words

                       c. Generally the first letter lowercase

   For example: int speed;

           boolean flag;

Second, the constants (the amount can not be changed)

       Defined variables, use the keyword final

       Traditionally constants are uppercase