How would I convert the numbers within my array list to negative numbers?

I’ve been trying to figure this out for like 20 minutes, and I still can’t figure it out.

I’m trying to get each individual positive number within listOfNumbers to be negative in order to create a bar graph. I can give more pieces of the code if needed, I’m just completely unsure of what to do.

public void plotLevels(ArrayList<Double> listOfNumbers) {
    int base = 350;
    int left = 50;
    int step = 25;
    UI.setColor(Color.black);

    for(int i = 0; i <listOfNumbers.size(); i++) {
        UI.fillRect(left, base, 20, (listOfNumbers.get(i)));
        left += step;
    }

>Solution :

If you want the number to be negative within the UI.fillRect, you can replace it with the following:

UI.fillRect(left, base, 20, (listOfNumbers.get(i) * -1));

Because you multiply the number with -1, it will become negavtive.