Enum

1.定义时使用enum关键字定义。

2.隐式继承了java.lang.Enum类，所以不能再继承其他类了。

3.隐式的final修饰符，所以不能被其他类继承。

 package enumTest;
 
 public enum Week {
     MONDAY,
     TUESDAY,
     WEDNESDAY,
     THURSDAY,
     FRIDAY,
     SATURDAY,
     SUNDAY;
 
     public static void main(String[] args)
     {
         Week day = Week.FRIDAY;
 
         switch(day)
         {
             case MONDAY:
                 System.out.println("it is Monday! work hard!");
                 break;
             case TUESDAY:
                 System.out.println("it is Tuesday! work hard hard!");
                 break;
             case WEDNESDAY:
                 System.out.println("it is Wednesday! tired!");
                 break;
             case THURSDAY:
                 System.out.println("it is Thursday! waiting weekend!");
                 break;
             case FRIDAY:
                 System.out.println("it is Friday! will have a nice night!");
                 break;
             case SATURDAY:
                 System.out.println("it is Saturday! lovely day!");
                 break;
             case SUNDAY:
                 System.out.println("it is monday!oh no tomorrow is Monday again!");
                 break;
             default:
                 System.out.println("it is monday! what!");
 
         }
     }
 }