medTable.setOnMouseClicked(new EventHandler<MouseEvent>() {
            @Override
            public void handle(MouseEvent event) {
                if (event.getClickCount() == 2) {

                    SellerData selectedData = medTable.getSelectionModel().getSelectedItem();
                    System.out.println(selectedData);
                    CheckData checkData = null;

                    if (mapChD.get(selectedData.getId()) == null) {
                        checkData = new CheckData();
                        System.out.println("no");
                        checkData.setId(selectedData.getId());
                        checkData.setMedName(selectedData.getMedName());
                        checkData.setCountOnSale(1);
                        checkData.setSalePrice(selectedData.getSalePrice());
                        price = selectedData.getSalePrice();
                        mapChD.put(selectedData.getId(), checkData);
                        System.out.println(mapChD.get(selectedData.getId()));

                    } else {
                        checkData = mapChD.get(selectedData.getId());
                        System.out.println(checkData.getCountOnSale());
                        int count = checkData.getCountOnSale() + 1;
                        System.out.println(count);

                        checkData.setCountOnSale(count);
                        checkData.setSalePrice(count * price);
                        mapChD.put(selectedData.getId(), checkData);
                        mapChD.replace(selectedData.getId(), checkData);
                        System.out.println("yes");
                        System.out.println(mapChD.get(selectedData.getId()));
                    }
                    checkTable.getItems().add(0, checkData);

                }
            }
        });

checkTable.getItems().add(0, checkData);