code: @Override
      public void paintCurrentValue(Graphics g, Rectangle bounds, boolean hasFocus) {
          ListCellRenderer renderer = comboBox.getRenderer();
          Component c;
  
          c = renderer.getListCellRendererComponent(listBox, comboBox.getSelectedItem(), -1, false, false);
  
          // Fix for 4238829: should lay out the JPanel.
          boolean shouldValidate = false;
          if (c instanceof JPanel) {
              shouldValidate = true;
          }
  
          if (c instanceof UIResource) {
              c.setName("ComboBox.renderer");
          }
  
          boolean force = forceOpaque && c instanceof JComponent;
          if (force) {
              ((JComponent) c).setOpaque(false);
          }
  
          int x = bounds.x, y = bounds.y, w = bounds.width, h = bounds.height;
          if (padding != null) {
              x = bounds.x + padding.left;
              y = bounds.y + padding.top;
              w = bounds.width - (padding.left + padding.right);
              h = bounds.height - (padding.top + padding.bottom);
          }
  
          currentValuePane.paintComponent(g, c, comboBox, x, y, w, h, shouldValidate);
  
          if (force) {
              ((JComponent) c).setOpaque(true);
          }
  
      }
docs: Paints the currently selected item.