Question

I have a function whose arguments are:

 myFn(String, List<Number>, List<Number>)

The calling function has two objects of List which I want to use as the 2nd and third argument of the function. I get the compilation error:

The method myFn(String, List<Number>, List<Number>) in the type MyLib is not applicable for the arguments (String, List<Double>, List<Double>)

Is there an easy way to overcome this? Is there an easy way to cast the list of Double into a List of Number?

Answer 1

You cannot cast List<Double> to a List<Number> because the following code would break your List<Double>

List<Double> list = new List<Double>();
List<Number> list1 = list; // This does not work
list1.add(new Integer(0));
Double d = list.get(0);// Hu-hoh you received an Integer, not a Double!!
List<? extends Number> list2 = list; // This does work

What you could do, is change

myFn(String, List<Number>, List<Number>)

to

myFn(String, List<? extends Number>, List<? extends Number>)