For this scenario, it looks like you can simply use an instance field.
public enum Direction {
NORTH(0x10), WEST(0x18), ...;
private final int code;
Direction(int code) { this.code = code; }
public int getCode() { return code; }
}
Java enum
are implemented as objects. They can have fields and methods. You also have the option of declaring a constructor that takes some arguments, and providing values for those arguments in your constant declaration. You can use these values to initialize any declared fields.
See also
Appendix: EnumSet
and EnumMap
Note that depending on what these values are, you may have an even better option than instance fields. That is, if you're trying to set up values for bit fields, you should just use an EnumSet
instead.
It is common to see powers of two constants in, say, C++, to be used in conjunction with bitwise operations as a compact representation of a set.
// "before" implementation, with bitwise operations
public static final int BUTTON_A = 0x01;
public static final int BUTTON_B = 0x02;
public static final int BUTTON_X = 0x04;
public static final int BUTTON_Y = 0x08;
int buttonState = BUTTON_A | BUTTON_X; // A & X are pressed!
if ((buttonState & BUTTON_B) != 0) ... // B is pressed...
With enum
and EnumSet
, this can look something like this:
// "after" implementation, with enum and EnumSet
enum Button { A, B, X, Y; }
Set<Button> buttonState = EnumSet.of(Button.A, Button.X); // A & X are pressed!
if (buttonState.contains(Button.B)) ... // B is pressed...
There is also EnumMap
that you may want to use. It's a Map
whose keys are enum
constants.
So, where as before you may have something like this:
// "before", with int constants and array indexing
public static final int JANUARY = 0; ...
Employee[] employeeOfTheMonth = ...
employeeOfTheMonth[JANUARY] = jamesBond;
Now you can have:
// "after", with enum and EnumMap
enum Month { JANUARY, ... }
Map<Month, Employee> employeeOfTheMonth = ...
employeeOfTheMonth.put(Month.JANUARY, jamesBond);
In Java, enum
is a very powerful abstraction which also works well with the Java Collections Framework.
See also
Related questions