code: private void addDateLabels() {
          dateLabels = new ArrayList<JLabel>();
          for (int i = 0; i < 42; ++i) {
              int dateLabelColumnX = ((i % 7)) + constantFirstDateLabelCell.x;
              int dateLabelRowY = ((i / 7) + constantFirstDateLabelCell.y);
              JLabel dateLabel = new JLabel();
              dateLabel.setHorizontalAlignment(SwingConstants.CENTER);
              dateLabel.setVerticalAlignment(SwingConstants.CENTER);
              dateLabel.setBackground(Color.white);
              dateLabel.setForeground(Color.black);
              dateLabel.setBorder(null);
              dateLabel.setOpaque(true);
              dateLabel.setText("" + i);
              CellConstraints constraints = CC.xy(dateLabelColumnX, dateLabelRowY);
              centerPanel.add(dateLabel, constraints);
              dateLabels.add(dateLabel);
              // Add a mouse click listener for every date label, even the blank ones.
              dateLabel.addMouseListener(new MouseLiberalAdapter() {
                  @Override
                  public void mouseLiberalClick(MouseEvent e) {
                      dateLabelMousePressed(e);
                  }
              });
          }
      }
docs: addDateLabels, This adds a set of 42 date labels to the calendar, and ties each of those
  labels to a mouse click event handler. The date labels are reused any time that the calendar
  is redrawn.
  
  This function should not depend on any settings variables.