What will be the output of the following Java program?

public class BoxDemo
{
    public static <U> void addBox(U u, java.util.List<Box<U>> boxes)
    {
       Box<U> box = new Box<>();
       box.set(u);
       boxes.add(box);
    }
    public static <U> void outputBoxes(java.util.List<Box<U>> boxes)
    {
        int counter = 0;
        for (Box<U> box: boxes)
        {
            U boxContents = box.get();
            System.out.println("Box #" + counter + " contains [" + boxContents.toString() + "]");
            counter++;
        }
    }
    public static void main(String[] args)
    {
        java.util.ArrayList<Box<Integer>> listOfIntegerBoxes = new java.util.ArrayList<>();
        BoxDemo.<Integer>addBox(Integer.valueOf(10), listOfIntegerBoxes);
        BoxDemo.outputBoxes(listOfIntegerBoxes);
    }
}