Enumerated Types - Introduction to Java Programming: Comprehensive Version - page 1285

9 System.out.println( "day2's ordinal is " + day2.ordinal());
10
11 System.out.println( "day1.equals(day2) returns " +
12 day1.equals(day2));
13 System.out.println( "day1.toString() returns " +
14 day1.toString());
15 System.out.println( "day1.compareTo(day2) returns " +
16 day1.compareTo(day2));

17 }
18 }
19
20 enum Day {SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY,
21

FRIDAY, SATURDAY}

An enumerated type can be defined inside a class, as shown in lines 2-3 in Listing I.1, or
standalone as shown in lines 20-21 Listing I.2. In the former case, the type is treated as an
inner class. After the program is compiled, a class named EnumeratedTypeDemo$Day.class
is created. In the latter case, the type is treated as a standalone class. After the program is
compiled, a class named Day.class is created.

Note
When an enumerated type is declared inside a class, the type must be declared as a
member of the class and cannot be declared inside a method. Furthermore, the type is
always static . For this reason, the static keyword in line 2 in Listing I.1 may be
omitted. The visibility modifiers on inner class can be also be applied to enumerated
types defined inside a class.

Tip
Using enumerated values (e.g., Day.MONDAY , Day.TUESDAY , and so on) rather than
literal integer values (e.g., 0, 1, and so on) can make program easier to read and maintain.

I.2 Using if or switch Statements with an
Enumerated Variable
An enumerated variable holds a value. Often your program needs to perform a specific action
depending on the value. For example, if the value is Day.MONDAY , play soccer; if the value is
Day.TUESDAY , take piano lesson, and so on. You can use an if statement or a switch state-
ment to test the value in the variable, as shown in (a) and (b)

if (day.equals(Day.MONDAY)) {
// process Monday

switch (day) {
case MONDAY:
// process Monday
break ;
case TUESDAY:
// process Tuesday
break ;
...
}

}
else if (day.equals(Day.TUESDAY)) {
// process Tuesday

Equivalent

}
else
...

(a)

(b)

In the switch statement in (b), the case label is an unqualified enumerated value (e.g.,
MONDAY , but not Day.MONDAY ).