This is a bit unusual; you are working off of input for the application command, but you do not appear to use any additional methods or object types. Casting and parsing isn't IMO something that should be learned before method handling.
The trick here is to simply ensure you have a double or Double to work with.
double dValues = new double[args.length];
for (int i = 0; i < args.length; ++i)
dValues[i] = Double.parseDouble(args[i]);
Simple as that. You now work with only dValues to collect the information about the count, max/min (easy via sorting a copy), average, sum, whatever you want.
Also, in the future please use [php][/php] or [code][/code] tags as it preserves the formatting.