Alfred’s Computing Weblog

Enum is an enumerated types, a special type in Java that used to hold static information.
Eg: the state of a connection (CONNECTING, CONNECTED, DISCONNECTED, etc), the day (MONDAY, TUESDAY, etc).
Besides of defining a status, we also can include some useful features of the Enum and write it as a method in the Enum.
Here is a simple example I write to show how to access to Enum’s method.

I have a Enum here, named “Day”:

package alfred.playground;

public enum Day {

	MONDAY, TUESDAY,
	WEDNESDAY, THURSDAY,
    FRIDAY, SATURDAY,
    SUNDAY;

	public boolean isWeekday() {
		return (equals(MONDAY) ||
				equals(TUESDAY) ||
				equals(WEDNESDAY) ||
				equals(THURSDAY) ||
				equals(FRIDAY));
	}

	public boolean isWeekend() {
		return (equals(SATURDAY) || equals(SUNDAY));
	}

}

And, here is the test program:

		Day day1 = Day.THURSDAY;
		System.out.println(String.format("[%s] is weekend? [%b]", day1, day1.isWeekend()));
		/*$>  [THURSDAY] is weekend? [false] */

		Day day2 = Day.SATURDAY;
		System.out.println(String.format("[%s] is weekend? [%b]", day2, day2.isWeekend()));
		/*$>  [SATURDAY] is weekend? [true] */

In order to call Enum’s method, we can not just directly call as usual class’s method “myClass.doSomething()”.
Instead, we must assign a value to the Enum before we can invoke the method.

For shorter codes, we can simplified the code by skipping the value assignment line:

		System.out.println(String.format("[%s] is weekend? [%b]", Day.FRIDAY, Day.FRIDAY.isWeekday()));
		/*$>  [FRIDAY] is weekday? [true] */