@Override
    public Class<?> getColumnClass(int columnIndex) {
        // Returns the class of each column
        if (columnIndex == columnNames.indexOf(ACTIVITY_COLUMN)) {
            return Integer.class;
        } else if (columnIndex == columnNames.indexOf(START_TIME_COLUMN)) {
            return Timestamp.class;
        } else if (columnIndex == columnNames.indexOf(END_TIME_COLUMN)) {
            return Timestamp.class;
        } else if (columnIndex == columnNames.indexOf(DURATION_COLUMN)) {
            return Long.class;
        } else if (columnIndex == columnNames.indexOf(DESCRIPTION_COLUMN)) {
            return String.class;
        } else {
            return Object.class;
        }
    }