Collection, enum or something else?

Todd <>
Wed, 23 Apr 2008 14:27:16 -0700 (PDT)

Suppose one has a class called Shrub that has well-defined behavior
and state. Now suppose one wants to create references (pardon the
loose wording, hopefully this will become clear shortly) to shrubs of
the world by continent.

One could extend the original Shrub class for each type of shrub and
then collect objects of the different shrubs in variables named by
continent, e.g., Collection NorthAmericanShrubs, etc. Or one could
declare an enum that uses the base shrub class as a constructor
argument, e.g.,

public enum NorthAmericanShrubs
    firstNAshrub( new Shrub( "firstNAshrub" ) ),
    secondNAshrub( new Shrub( "secondNAshrub" ) );

    public NorthAmericanShrubs( Shrub shrub )
        this.shrub = shrub;

    private Shrub shrub = null;

In some ways, the enum is cleaner as it doesn't require multiple
classes that would only be different by constructor (each shrub
type), however, I can't access 'shrub' directly as firstNAshrub is
of type NorthAmericanShrubs, not type Shrub.

Without the addition of a getter method, I don't have access to
 Shrub behavior, but that adds undesirable complexity such as
 when one might want to iterate over the shrubs:

for( NorthAmericanShrubs naShrub : NorthAmericanShrubs.values() )
    Shrub shrub = naShrub.getShrub();

    // do something here

Is there something cleaner than multiple, essentially identical
classes or the enum construct? Or am I just being too picky
about not being able to access Shrub behavior directly through
my enum (as if the enum extended a type)? Or is this an
instance where abstracting out an interface for both Shrub and
NorthAmericanShrubs is appropriate (which would then create
object delegation code)?


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