Declaring fields inside enum type

enum types in Java are much powerful and you can declare fields in addition to constants.

enum Month{
 JANUARY(1, "31 Days"),
 FEBRUARY(2, "28 or 29 Days"),
 MARCH(3, "31 Days"),
 APRIL(4, "30 days"),
 MAY(5, "31 Days"),
 JUNE(6, "30 Days"),
 JULY(7, "31 Days"),
 AUGUST(8, "31 Days"),
 SEPTEMBER(9, "30 Days"),
 OCTOBER(10, "31 Days"),
 NOVEMBER(11, "30 Days"),
 DECEMBER(12, "31 Days");
 
 int num;
 String msg;
 
 Month(int num, String msg){
  this.num = num;
  this.msg = msg;
 }
 
 public static void main(String args[]){
  for(Month m : Month.values()){
      System.out.println(m.num +" "+ m +" "+ m.msg);
  }
 }
}

Output

1 JANUARY 31 Days
2 FEBRUARY 28 or 29 Days
3 MARCH 31 Days
4 APRIL 30 days
5 MAY 31 Days
6 JUNE 30 Days
7 JULY 31 Days
8 AUGUST 31 Days
9 SEPTEMBER 30 Days
10 OCTOBER 31 Days
11 NOVEMBER 30 Days
12 DECEMBER 31 Days

Compiler automatically adds some special methods when it creates enum. For example, enum have a static values method that returns an array containing all of the values of the enum in the order they are declared.

Note: constructor for enum type must be package-private or private access. It automatically creates the constants that are defined at the beginning of the enum body. You cannot invoke an enum constructor directly. 

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