Java Reference
In-Depth Information
public static void main(String[] args) {
// Define three variables of type Day
Day yesterday = Day.Thursday;
Day today = Day.Friday;
Day tomorrow = Day.Saturday;
// Output the values of the Day variables
System.out.println("Today is " + today);
System.out.println("Tomorrow will be " + tomorrow);
System.out.println("Yesterday was " + yesterday);
}
}
This produces the output:
Today is Friday
Tomorrow will be Saturday
Yesterday was Thursday
How It Works
The code itself is essentially what you saw in the previous section. There is the declaration of the enu-
merated type,
Day
, with definitions of three variables of that type in
main()
. You then have output state-
ments for the values of the three variables. Note that
enum
types cannot be local to a method. If you put
the definition for the
Day
type within
main()
, the example does not compile. Here the
Day
type is local to
the class
TryEnumeration
that contains the
main()
method. You could put the definition for
Day
outside
the
TryEnumeration
class, in which case it is global.
The output is very interesting. It doesn't display the numerical values of the variables of type
Day
but
their names. This is the default way in which a value of an enumeration type is represented as a string
because the names are more important than the values in most enumeration types. After all, the values
that they have serve only to differentiate one enumeration constant from another.
This is just a small fraction of the capabilities of enumerations. I introduced the concept at this point
because enumeration constants — the values that a variable of an enumeration type may have — are al-
ways integers. You will find out more about how you can use them as you progress through subsequent
chapters, but you have to wait until Chapter 6 for the full story.
BOOLEAN VARIABLES
Variables of type
boolean
can have only one of two values,
true
or
false
. The values
true
and
false
are
boolean
literals. The
boolean
type is named after the mathematician, George Boole, who invented Boolean
algebra, and variables of this type are described as
boolean
variables. You can define a variable of type
boolean
called
state
with the following statement:
boolean state = true;
This statement also initializes the variable
state
with the value
true
.
You can also set the value of a
boolean
variable in an assignment statement. For example, the statement
