Operations on Lists of Numbers

Question

I've come across a problem in my code that could have a few different solutions.
First, the problem. This is the code:
     public static List<List<?>> linear_solve(List<List<Double>> m, List<Double> v) throws Exception {
          if(m.size() != v.size()){
               throw new Exception("Incompatible system.");
          List<List<Double>> solution = new ArrayList<List<Double>>(m);
          List<List<?>> result = new ArrayList<List<?>>();
          //Add the values from v onto n
          for(int row = 0; row < solution.size(); row++)
               solution.get(row).add(v.get(row));An error is generated on the last line, when v is of type List<Integer>. This is the error:
java.lang.ClassCastException: java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.DoubleWhat confuses me the most here, is why this error is showing up so late. I would assume that the error would be when the program attempts to pass a List<Integer> into a List<Double>.
I have several different functions that behave in the same way, so I'd like to find the most elegant solution. I've thought of simply accepting List<Number>, but I need to be able to use the * operator, which is defined for both Integer and Double, but is not defined for Number. Is it possible, at all, to do this?
Another solution would be to simply cast it, but I can't think of how to do this.
Any help is greatly appreciated.

Answer 1

By the way, the forum software likes to add '>' characters to our posts, as you may have noticed. You can avoid that problem by always using the &lt; escape for the '<' character, or making sure it isn't followed immediately by a letter:   List<List<Double>> solution = new ArrayList< List< Double>>(m); The problem only occurs if the software sees another '<' before the next '>'; it seems to think it's closing our HTML tags for us.