@Override
    public void focusLost(FocusEvent fe) {
        //System.out.println("Focus lost!");
        JTextField thisField = (JTextField) fe.getSource();
        try {
            int inputNumber = Integer.parseInt(thisField.getText());
            //System.out.print("Parsed: ");
            //System.out.println(inputNumber);

            //If the user entered a wrong mark, e.g. 16
            if (inputNumber < 0 || inputNumber > 15) {
                setMarkInputFieldHighlight(thisField, HighlightMode.NUM_ERROR);
            } else {
                setMarkInputFieldHighlight(thisField, HighlightMode.NONE);
            }
        } catch (NumberFormatException e) {
            if (thisField.getText().equals("")) {
                setMarkInputFieldHighlight(thisField, HighlightMode.NONE);              //No input
            } else {
                setMarkInputFieldHighlight(thisField, HighlightMode.INVALID_INPUT);      //If the input is non-numerical and not empty
            }
        }

    }