Re: generics array type check

From:

=?ISO-8859-1?Q?Arne_Vajh=F8j?= <arne@vajhoej.dk>

Newsgroups:

comp.lang.java.programmer

Date:

Fri, 25 Jul 2014 21:12:56 -0400

Message-ID:

<53d30099$0$305$14726298@news.sunsite.dk>

On 7/24/2014 4:03 AM, Philipp Kraus wrote:

I have got this signature of a method private static <T> long[] getSize(
T p_data )
Depend on the type T the return value is changes e.g. on a non-array type

getSize( 5 ) => new long[1]{1}
getSize( "test" ) => new long[1]{1}

on an array it should return

double[] p_array
getSize( p_array ) => new long[1]{ p_data.length }

and on 2-dimensional array it should be
double[][] p_array
getSize( p_array ) => new long[2]{ p_array.length, p_array[0].length }

How can I check the generic data type in a correct way to detect the
array type?

I don't think the generic type information provide any benefits - you
are stuck with reflection.

For inspiration:

    public static List<Integer> getDim(Object obj) {
        List<Integer> res = new ArrayList<>();
        Object currobj = obj;
        Class<?> clz = obj.getClass();
        while(clz != null) {
            if(clz.isArray()) {
                res.add(Array.getLength(currobj));
                currobj = Array.get(currobj, 0);
            }
            clz = clz.getComponentType();
        }
        return res;
    }

Note that I have made 2 changes:
- return List<Integer> instead of int[]
- return a zero length collection for non arrays to enable to
   distinguish between non arrays and arrays with 1 element

Arne

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