code: private void createPageControls() {
          WizardPage[] pages = wizard.getPages();
          for (int i = 0; i < pages.length; i++) {
              JComponent c = pages[i].getControl();
              GuiStandardUtils.attachDialogBorder(c);
              Dimension size = c.getPreferredSize();
              if (size.width > largestPageWidth) {
                  largestPageWidth = size.width;
              }
              if (size.height > largestPageHeight) {
                  largestPageHeight = size.height;
              }
          }
      }
docs: Allow the wizard's pages to pre-create their page controls. This allows
  the wizard dialog to open to the correct size.