Parameterized Types and Generic Classes

Question

I am having trouble sending my arraylist as a param to a generic method. Any idea what im doing wrong here?

ArrayList<Integer> list50k = new ArrayList<>();
list50k.add(1);
list50k.add(5);
list50k.add(8);
list50k.add(7);

selectionSort(list50k); // error is in this line

I then try to send the array to the method and get an error. here is the method:

public static <T extends Comparable<T>> void selectionSort(T[] list){...}

Answer 1

The problem is that ArrayList<T> is not an array, meaning it can't be converted to a T[] .

Your method signature could be selectionSort(List<T>) if you wanted to pass the ArrayList .

You could also convert the ArrayList to a T[] but the syntax for that is a little annoying in java and I don't recommended unless you really need an array.

Answer 2

Try this one

selectionSort(list50k.toArray(new Integer[list50k.size()])); 

get Integer[] from ArrayList<Integer> to make it valid argument as per your method signature.