On Wed, 17 Jun 2026 08:54:10 GMT, Marius Hanl <[email protected]> wrote:
> This PR is an optimization for `Node.styleClass` and `Parent.stylesheets`. > Instead of always initializing both properties with an empty list, we are > creating (therefore allocating) the list on the first access instead. > Similar to many other lazy properties. > > Why? > - `Parent.getStylesheets()` is very rarely used by developers and JavaFX > code. So this list is very often completely unused and empty. Most developers > usually only add stylesheets at the `Scene` > - `Node.getStyleClass()` is usually not used (empty) for layout containers > such as `Pane` or `Group`. A JavaFX App usually consists of a good amount of > such containers > > So that our CSS code is not initializing both lists on access, I added > related `NodeHelper` and `ParentHelper` methods to return `null` when both > lists were not initialized and therefore used. Otherwise we return the list > as before. > This will save us some memory and allocation, which is both good for the > memory consumption but also for `Node` / `Parent` creation (time). > > Added documentation and tests. Will do some measurements with some apps very > soon and attach it here. > > --- > > # Benchmarks > > I wrote a very small scene graph analyzer snippet to measure the memory gain. > Feel free to test this on your own apps! > 1. Get the `SceneGraphAnalyzer` here: > [SceneGraphAnalyzer](https://gist.github.com/Maran23/38beca5b043e547e1a84749e3162c0b2) > 2. Add this code to your `Scene` and press the shortcut `F12` when all of the > UI is loaded: > > scene.setOnKeyPressed(event -> { > if (event.getCode() == KeyCode.F12) { > var analyzer = new SceneGraphAnalyzer(); > var res = analyzer.analyze(scene); > res.print(); > } > }); > > 3. If you have a modular app, add the following VM argument: `--add-opens > javafx.graphics/javafx.scene=yourapp` > > ## Projects > > 1. Tested with > [JFXCentral](https://github.com/dlsc-software-consulting-gmbh/jfxcentral2) > > > ╔══════════════════════════════════════════════════╗ > ║ Scene Graph Analysis ║ > ╠══════════════════════════════════════════════════╣ > ║ Total nodes: 654 ║ > ║ ├─ Parent nodes: 388 ║ > ║ └─ Leaf nodes: 266 ║ > ╠══════════════════════════════════════════════════╣ > ║ Null styleClass: 19 / 654 ( 2.9%) ║ > ║ Null stylesheets: 386 / 388 ( 99.5%) ║ > ╠══════════════════════════════════════════════════╣ > ║ Saved (styleClass): 1.34 K... Today I learned about https://github.com/openjdk/jol to measure the exact memory footprint of objects and used those insights to measure the memory gain of some apps - results in the PR description. Memory stats: com.sun.javafx.collections.ObservableListWrapper@76bbca23d footprint: COUNT AVG SUM DESCRIPTION 1 16 16 [Ljava.lang.Object; 1 40 40 com.sun.javafx.collections.ObservableListWrapper 1 24 24 java.util.ArrayList 3 80 (total) With `-XX:+UseCompactObjectHeaders` (always enabled in JDK-27, so used this value as baseline): com.sun.javafx.collections.ObservableListWrapper@7ffb7d94d footprint: COUNT AVG SUM DESCRIPTION 1 16 16 [Ljava.lang.Object; 1 32 32 com.sun.javafx.collections.ObservableListWrapper 1 24 24 java.util.ArrayList 3 72 (total) ------------- PR Comment: https://git.openjdk.org/jfx/pull/2191#issuecomment-4735606589
