Re: Initializing a Map in an Interface?
Rhino wrote:
Is it possible to do a full-on assignment of specific values to a HashMap
in an interface? If so, how?
I'd like to create a HashMap that has a key that is a String and a value
that is a Color. The HashMap would contain a substantial number of these
entries.
I'm trying to figure out how to write the initialization but am confusing
myself with respect to brackets, braces, commas, etc.
Defining it as an Object[][] is easy enough:
public static final Object[][] EIGHT_BIT_=
COLORS = {
Lighten up on the indentation for Usenet listings to keep them
readable. Four spaces is a comfortable maximum per indent level.
{"Black", new Color(0,0,0=
)},
{"Obscure Gray", new Colo=
r(51, 51, 51)},
{"Dark Gray", new Color(1=
02, 102, 102)},
{"Light Gray", new Color(=
153, 153, 153)},
{"Pale Gray", new Color(2=
04, 204, 204)},
{"White", new Color(255, =
255,255)}
};
How could I write the definition if I want the Object[][] to be a HashMap
<String, Color>?
I'm guessing that defining the Map/HashMap explicitly like this isn't
possible and that I have to initialize it with code like this:
Map<Color, String> colorsToNamesMap = n=
ew HashMap<Color,
String>();
for (int ix=0; ix<EIGHT_BIT_COLORS.leng=
th; ix++) {
colorsToNamesMap.put((Col=
or)EIGHT_BIT_COLORS[ix][1],
(String)EIGHT_BIT_COLORS[ix][0]);
}
which means I can't define the Map in an interface because this sort of
code can't appear in an Interface, only a Class.
You really shouldn't be putting implementation in an interface in the
first place. If the intent is to create a static final immutable Map,
put it in a utility class with a static initializer to set up the
map. (A utility class is a class with a private no-arg constructor
and otherwise no non-static elements.) You can then use 'import
static' or the FQN to bring that Map into another type definition
(e.g., for an interface, despite that being an antipattern), either as
a 'Map' variable or the return value of a static method of the utility
class.
Untested, imports omitted:
public class Util
{
private Util(){}
public static final Map <Color, String> COLOR_NAMES;
static
{
Map <Color, String> colors = new HashMap <Color, String> ();
colors.put( Color.BLACK, "Black" );
colors.put( new Color(51, 51, 51), "Obscure Gray" );
// ...
colors.put( Color.WHITE, "White" );
COLOR_NAMES = Collections.unmodifiableMap( colors );
}
}
public interface AntipatternContainsImplementation
{
Map <Color, String> colorsToNames = Util.COLOR_NAMES;
}
--
Lew