Sum ArrayList to integer

Question

I am trying to sum up an ArrayList to an integer.

On the sum += list.get(i); line I get an error:

The operator += is undefined for the argument type(s) double, Object

JTable j = new JTable(data, columnNames);
List<Object> list = new ArrayList<>();

for (i = 0; i < j.getModel().getRowCount(); i++) {
    list.add(j.getModel().getValueAt(i, 1));
}
int sum = 0;
for (int i = 0; i < list.size(); i++) {
    sum += list.get(i);
}

System.out.println(sum);

What can I do to sum up the ArrayList to an integer?

Answer 1

getValueAt returns an Object. If you know it's an Integer, you need to explicitly cast it so that Java can treat it as such. E.g.:

List<Integer> list = new ArrayList<>();
for(i = 0;i<j.getModel().getRowCount();i++)
{
    list.add((Integer) j.getModel().getValueAt(i,1));
}

Now that list is a List<Integer>, list.get will return an Integer, not an Object, and your second for loop should work just fine.

EDIT:
According to the comment, the value in model is actually a String not an Integer. You'll have to convert it to an Integer yourself:

List<Integer> list = new ArrayList<>();
for(i = 0;i<j.getModel().getRowCount();i++)
{
    list.add(Integer.valueOf((String) j.getModel().getValueAt(i,1)));
}