I've found the solution :
levelChoice = FXCollections.observableArrayList("Bla", "Blo");
levelColumn.setCellValueFactory(
new PropertyValueFactory<ClassesProperty, String>("level")
);
levelColumn.setCellFactory(ComboBoxTableCell.forTableColumn(levelChoice));
levelColumn.setOnEditCommit(
new EventHandler<CellEditEvent<ClassesProperty, String>>() {
@Override
public void handle(CellEditEvent<ClassesProperty, String> t) {
((ClassesProperty) t.getTableView().getItems().get(t.getTablePosition().getRow())).setLevel(t.getNewValue());
};
}
);