Java: Dynamic type casting using enums

Question

I am trying to do something along the lines of:

public void setContents(Object[] values)
{
    ...

        //A. this works
        mRank =
            ((String)(values[Columns.RANK.index])); 

        //B. doesn't work (entire line underlined by netbeans)
        mRank =
            (Columns.RANK.type.cast(values[Columns.RANK.index]));
        //incompatible types: required java,lang.String found: java.lang.Object

        //C. doesn't work (first RANK is underlined by netbeans)
        mRank =
            ((Columns.RANK.type)(values[Columns.RANK.index]));
        //cannot find symbol symbol: class RANK location: blah.blah.Columns

    ...
}

Where columns is an inner enum, like so:

public static enum Columns
{

    RANK(0, "Rank", String.class),
    NUMBER(1, "Number", Integer.class);

    public String text;
    public Class type;
    public int index;

    private Columns(int idx, String text, Class clasz)
    {
        this.type = clasz;
        this.text = text;
        this.index = idx;
    }
}

I understand why line B doesn't work, but what I don't get is why C doesn't work. If I use Columns.RANK.type anywhere else other than in a type cast, it works fine, but one I attempt to do a typecast with the class, it compiles saying it cannot find RANK in the enum, which shouldn't be the case.

How to work around?

Thanks!

Answer 1

C doesn't work, because Columns.RANK.type is not accessible at compile time.

However, B can be implemented using a custom generic-based class instead of enum:

class Columns<T>
{
    public static final Columns<String> RANK = new Columns<String>(0, "Rank", String.class);
    public static final Columns<Integer> NUMBER = new Columns<Integer>(1, "Number", Integer.class);

    public final Class<T> type;
    public final String text; 
    public final int index; 

    private Columns(int idx, String text, Class<T> clasz) 
    { 
        this.type = clasz; 
        this.text = text; 
        this.index = idx; 
    } 
}