尝试理解枚举

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");
    }
    
}