TableView<HashMap<String, String>> tableView;

 ObservableList<TableColumn<HashMap<String, String>, String>> tvcolumns = FXCollections.observableArrayList();

        tableColumns.forEach((t) -> {
            tvcolumns.add(new TableColumn<>(t));
        });

        for (int i = 0; i < tvcolumns.size(); i++) {
            TableColumn<HashMap<String, String>, String> temp = tvcolumns.get(i);
            temp.setCellValueFactory(new PropertyValueFactory<>(keySet.get(i)));
        }

        tableView.getItems().clear();
        tableView.setItems(tableData);
        tableView.getColumns().addAll(tvcolumns);

public class MainUiController implements Initializable {

    @FXML
    private AnchorPane rootPane;
    @FXML
    private VBox vBoxMain;
    @FXML
    private HBox hBoxTop;
    @FXML
    private VBox vBoxTopLeft;
    @FXML
    private ComboBox<String> cbCatalog;
    @FXML
    private VBox vBoxTopRight;
    @FXML
    private ComboBox<String> cbTables;
    @FXML
    private HBox hBoxBottom;
    @FXML
    private TitledPane titledPaneBottom;
    @FXML
    private AnchorPane anchorPaneBottom;
    @FXML
    private TableView<HashMap<String, String>> tableView;

    DBHelper dbHelper = new DBHelper();

    /**
     * Initializes the controller class.
     *
     * @param url
     * @param rb
     */
    @Override
    public void initialize(URL url, ResourceBundle rb) {
        // TODO
        ObservableList<String> catalogItems = cbCatalog.getItems();
        catalogItems.clear();
        catalogItems.addAll(dbHelper.getCatalogs());
        titledPaneBottom.setExpanded(false);
    }

    @FXML
    private void populateTables(ActionEvent event) {
        String dbName = ((ComboBox<String>) event.getSource()).getValue();
        System.out.println("catalog value: " + dbName);
        dbHelper.useDB(dbName);
        ObservableList<String> tables = cbTables.getItems();
        tables.clear();
        tables.addAll(dbHelper.getTables());
    }

    @FXML
    private void descTable(ActionEvent event) {
        String tableName = ((ComboBox<String>) event.getSource()).getValue();

        ObservableList<String> tableColumns = dbHelper.getTableColumns(tableName);
        ObservableList<HashMap<String, String>> tableData = dbHelper.getTableData();

        List<String> keySet = null;
        if (!tableData.isEmpty()) {
            keySet = new ArrayList<>(tableData.get(0).keySet());
        }

        titledPaneBottom.setText(""" + tableName + "" description:");

        ObservableList<TableColumn<HashMap<String, String>, String>> tvcolumns = FXCollections.observableArrayList();

        tableColumns.forEach((t) -> {
            tvcolumns.add(new TableColumn<>(t));
        });

        for (int i = 0; i < tvcolumns.size(); i++) {
            TableColumn<HashMap<String, String>, String> temp = tvcolumns.get(i);
            temp.setCellValueFactory(new PropertyValueFactory<>(keySet.get(i)));
        }

        tableView.getItems().clear();
        tableView.setItems(tableData);
        tableView.getColumns().addAll(tvcolumns);
    }
}

class DBHelper {

    Connection con;
    Statement st;
    ObservableList<String> tablesList = FXCollections.observableArrayList();
    ObservableList<String> columnList = FXCollections.observableArrayList();
    HashMap<String, String> tableData;
    ObservableList<HashMap<String, String>> tableDataList = FXCollections.observableArrayList();
    String dbName, tableName;
    ResultSet tableCols;
    ResultSetMetaData colsMetaData;

    public DBHelper() {
        try {
            con = DriverManager.getConnection("jdbc:mysql://localhost:3306/", "*****", "******");
            st = con.createStatement();
        } catch (SQLException ex) {
            Logger.getLogger(DBHelper.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    public ObservableList<String> getCatalogs() {
        try {
            ObservableList<String> catalogList = FXCollections.observableArrayList();
            DatabaseMetaData dbmd = con.getMetaData();
            ResultSet catalogs = dbmd.getCatalogs();
            while (catalogs.next()) {
                catalogList.add(catalogs.getString(1));
            }
            return catalogList;
        } catch (SQLException ex) {
            Logger.getLogger(DBHelper.class.getName()).log(Level.SEVERE, null, ex);
        }
        return null;
    }

    public ObservableList<String> getTables() {
        try {
            ResultSet tables = st.executeQuery("show tables");
            tablesList.clear();
            while (tables.next()) {
                tablesList.add(tables.getString(1));
            }
            return tablesList;
        } catch (SQLException ex) {
            Logger.getLogger(DBHelper.class.getName()).log(Level.SEVERE, null, ex);
        }
        return null;
    }

    void useDB(String dbName) {
        this.dbName = dbName;
        try {
            int execute = st.executeUpdate("use " + dbName);
        } catch (SQLException ex) {
            Logger.getLogger(DBHelper.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    public ObservableList<String> getTableColumns(String tableName) {
        this.tableName = tableName;
        try {
            tableCols = st.executeQuery("desc " + tableName);
            colsMetaData = tableCols.getMetaData();
            columnList.clear();
            int count = 1;
            while (count <= colsMetaData.getColumnCount()) {
                columnList.add(colsMetaData.getColumnName(count));
                count++;
            }
            return columnList;
        } catch (SQLException ex) {
            Logger.getLogger(DBHelper.class.getName()).log(Level.SEVERE, null, ex);
        }
        return null;
    }

    public ObservableList<HashMap<String, String>> getTableData() {
        tableDataList.clear();
        if (tableCols != null & colsMetaData != null) {
            try {
                while (tableCols.next()) {
                    tableData = new HashMap<>();
                    int count = 1;
                    while (count <= colsMetaData.getColumnCount()) {
                        tableData.put(colsMetaData.getColumnName(count), tableCols.getString(count));
                        count++;
                    }
                    tableDataList.add(tableData);
                }
                tableCols.close();
                tableCols = null;
                colsMetaData = null;
                return tableDataList;
            } catch (SQLException ex) {
                Logger.getLogger(DBHelper.class.getName()).log(Level.SEVERE, null, ex);
            }
        }
        return null;
    }

}