package enumtest;public class EnumTest {    public static void main(String[] args) {        WeekDay day = WeekDay.SUN;        System.out.println(day.nextDay());    }}//先模拟一个 枚举 （说明白,枚举形成的基本思路）abstract class WeekDay{    private WeekDay(){}  //上来就把它的构造器私有化,因为枚举的实例是固定的        public static final WeekDay MON = new WeekDay(){ //定义(成员)内部类        @Override        public WeekDay nextDay()         {            return WeekDay.SUN;        }            };    public static final WeekDay SUN = new WeekDay(){        @Override        public WeekDay nextDay()         {            return WeekDay.MON;        }    };        public abstract WeekDay nextDay();        @Override    public String toString()    {        return this==SUN?"SUN":"MON";    }}

package enumtest;public class EnumTest {    public static void main(String[] args) {        WeekDay day = WeekDay.SUN;        System.out.println(day);        System.out.println(day.name());        System.out.println(day.ordinal()); //枚举实例在枚举类中的位置        System.out.println(day.toString());        System.out.println(WeekDay.valueOf("MON"));    }}enum WeekDay{    SUN,MON(),THU(1),WES,THR,FRI,SAT;    //构造方法只能私有化    private WeekDay()    {        System.out.println("调用了无参构造器...");    }      private WeekDay(int i)    {        System.out.println("调用了有参构造器");    }    }