枚举

public abstract class WeekDay {
    private WeekDay(){}
    private final static WeekDay MON=new WeekDay(){

        @Override
        public WeekDay nextday() {
            // TODO Auto-generated method stub
            return SUN;
        }
        
    };
    final static WeekDay SUN=new WeekDay(){

        @Override
        public WeekDay nextday() {
            // TODO Auto-generated method stub
            return MON;
        }
        
    };
    
    public abstract WeekDay nextday();
//    public WeekDay nextDay()
//    {
//        if(this==SUN)
//        {
//            return Mon;
//        }else{
//            return SUN;
//        }
//    }
    public String toString()
    {
        return this==SUN?"sun":"mon";
    }
}

public class numerDemo {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        WeekDay weekDay=WeekDay.SUN;
        System.out.println(weekDay.nextday());
        ==========================================================//调用上面的WeekDay
        WeekDay1 weekDay2=WeekDay1.FRI;
        System.out.println(weekDay2.name());
        System.out.println(weekDay2.ordinal());
        System.out.println(weekDay2.getClass());
        System.out.println(WeekDay1.valueOf("SUN"));
        System.out.println(WeekDay1.values().length);
    }
    
    public enum WeekDay1{
        SUN,MON,TUE,WED,THI,FRI,SAT
    }
}

枚举的抽象的应用
package numDemo;

public class EnumTest {

    public static void main(String[] args) {
        
        WeekDay weekDay2=WeekDay.FRI;
    }
    public enum WeekDay{
        SUN(1),MON,TUE,WEN,THT,FRI,SAT;
        private WeekDay(){
            System.out.println("first");}
        private WeekDay(int day){
            System.out.println("second");
            }
    }
    public enum TrafficLamp{
        RED(30){

            @Override
            public TrafficLamp nextlamp() {
                // TODO Auto-generated method stub
                return GREEN;
            }
            
        },
        GREEN(45){

            @Override
            public TrafficLamp nextlamp() {
                // TODO Auto-generated method stub
                return YELLOW;
            }
            
        },
        YELLOW(5){

            @Override
            public TrafficLamp nextlamp() {
                // TODO Auto-generated method stub
                return RED;
            }
            
        };
        public abstract TrafficLamp nextlamp();
        private int time;
        private TrafficLamp(int time){this.time=time;};
    }

}