@Order(10.0)
public class MainBox extends AbstractGroupBox {

    @Override
    protected void injectFieldsInternal(List<IFormField> fieldList) {

      //int params = this.reportId.intValue();
      int params = 1;

      for (int i = 1; i < params; i++) {
        final int param = i;
        fieldList.add(new AbstractStringField() {
          @Override
          protected String getConfiguredLabel() {
            return "Field " + param;
          }
        });
      }
    }

    @Order(10.0)
    public class OkButton extends AbstractOkButton {
    }

    @Order(20.0)
    public class CancelButton extends AbstractCancelButton {
    }
 }

@Order(30.0)
public class GenerateReportWithParametersMenu extends AbstractMenu {

    @Override
    protected String getConfiguredText() {
    return TEXTS.get("ProduceerRapportMetParameters");
    }

    @Override
    protected void execAction() throws ProcessingException {

    Long reportId = getTable().getReportIDColumn().getSelectedValue();
    GenericForm form = new GenericForm(reportId);
    form.setGenericFormNr(reportId);
    form.startModify();
    form.waitFor();
    if (form.isFormStored()) {
        reloadPage();
      }
    }
}

public class GenericForm extends AbstractForm{
 private int m_myParam;

 public GenericForm(int myParam){
  super(false);//false=do not yet initialize the form
  m_myParam=myParam;
  callInitializer();//now init the form, this will inject the fields etc.
 }

 //use m_myParam inside the MainBox inject

}