Summary

Paint and Material cannot be extended by user code and will be sealed.

Problem

None of these classes can be extended by user code, because both classes either have a package-private constructor, or package-private abstract methods. Sealing these classes allows us to use exhaustive pattern matching.

Solution

Both classes can be compatibly sealed, since existing language rules prevent classes outside of the javafx.scene.paint package to extend Paint or Material.

Specification

--- a/modules/javafx.graphics/src/main/java/javafx/scene/paint/Paint.java
+++ b/modules/javafx.graphics/src/main/java/javafx/scene/paint/Paint.java
@@ -45,7 +45,8 @@
  *
  * @since JavaFX 2.0
  */
-public abstract class Paint implements Interpolatable<Paint> {
+public abstract sealed class Paint implements Interpolatable<Paint>
+                                   permits Color, LinearGradient, RadialGradient, ImagePattern {

     static {
         Toolkit.setPaintAccessor(new Toolkit.PaintAccessor() {

--- a/modules/javafx.graphics/src/main/java/javafx/scene/paint/Material.java
+++ b/modules/javafx.graphics/src/main/java/javafx/scene/paint/Material.java
@@ -45,7 +45,7 @@
  *
  * @since JavaFX 8.0
  */
-public abstract class Material {
+public abstract sealed class Material permits PhongMaterial {

     static {
         // This is used by classes in different packages to get access to