您好，在以下代码中，请问this.day=day 在下面是什么意思?

Question

public enum WeekDay { 
Mon("Monday"), Tue("Tuesday"), Wed("Wednesday"), Thu("Thursday"), Fri( 
"Friday"), Sat("Saturday"), Sun("Sunday"); 

/**定义枚举类型自己的属性**/ 
private final String day; 

private WeekDay(String day) { 
this.day = day; 
} 

/**定义枚举类型自己的方法**/ 
public static void printDay(int i){ 
switch(i){ 
case 1: System.out.println(WeekDay.Mon); break; 
case 2: System.out.println(WeekDay.Tue);break; 
case 3: System.out.println(WeekDay.Wed);break; 
case 4: System.out.println(WeekDay.Thu);break; 
case 5: System.out.println(WeekDay.Fri);break; 
case 6: System.out.println(WeekDay.Sat);break; 
case 7: System.out.println(WeekDay.Sun);break; 
default:System.out.println("wrong number!"); 
} 
} 

public String getDay() { 
return day; 
} 
}