With this sample code based on empty ObservableList, the columns not growing. With two row-items, the columns are growing but threre is a third empty, useless "column" in the table visible.

public void start(Stage primaryStage) throws Exception {
        Group rootGroup = new Group();
        Scene scene = new Scene(rootGroup, 800, 600);
 
        primaryStage.setScene(scene);
 
        ObservableList<Dimension> testItems = FXCollections.observableArrayList();
        //testItems.add(new Dimension(100, 200));
        //testItems.add(new Dimension(300, 400));
 
        TableView<Dimension> table = new TableView<Dimension>();
        table.setItems(testItems);
 
        TableColumn<String> testColumn = new TableColumn<String>("Width");
        testColumn.setResizable(true);
        testColumn.setProperty("width");
        testColumn.setMinWidth(100);
 
        TableColumn<String> testColumn2 = new TableColumn<String>("Height");
        testColumn2.setResizable(true);
        testColumn2.setProperty("height");
        testColumn2.setMinWidth(100);
 
        table.getColumns().addAll(testColumn, testColumn2);
        table.setColumnResizePolicy(TableView.CONSTRAINED_RESIZE_POLICY);
 
        BorderPane mainPane = new BorderPane();
        mainPane.setCenter(table);
 
        scene.setRoot(mainPane);
 
        primaryStage.centerOnScreen();
        primaryStage.setVisible(true);
    }