Fixed memory leak in smooth scrolling due to multiple notifications.

Author: Chrriis

flatlaf-core/src/main/java/com/formdev/flatlaf/SmoothScrollingHelper.java

@@ -16,8 +16,9 @@
 import java.awt.event.ComponentEvent;
 import java.awt.event.KeyEvent;
 import java.awt.event.MouseEvent;
-import java.util.ArrayList;
-import java.util.List;
+import java.util.Collections;
+import java.util.IdentityHashMap;
+import java.util.Set;
 import javax.swing.JComponent;
 import javax.swing.JScrollBar;
 import javax.swing.JScrollPane;
@@ -72,7 +73,7 @@ public void eventDispatched( AWTEvent event ) {
 					boolean isBlitScrollModeBlocked_ = isBlitScrollModeBlocked;
 					if(!isBlitScrollModeBlocked_) {
 						Component c = ((ComponentEvent)event).getComponent();
-						for( JViewport viewport: viewportList ) {
+						for( JViewport viewport: viewportSet ) {
 							Container scrollPane = viewport.getParent();
 							if(scrollPane == c || scrollPane.isAncestorOf( c )) {
 								setInSmoothScrolling( viewport, true );
@@ -83,7 +84,7 @@ public void eventDispatched( AWTEvent event ) {
 					}
 					if( !isHoldingScrollModeBlocked && ( !isBlitScrollModeBlocked_ || event.getID() == MouseEvent.MOUSE_RELEASED )) {
 						SwingUtilities.invokeLater( () -> {
-							for( JViewport viewport: viewportList ) {
+							for( JViewport viewport: viewportSet ) {
 								setBlitScrollModeBlocked( viewport, false );
 								setInSmoothScrolling( viewport, false );
 							}
@@ -171,13 +172,13 @@ private static synchronized void setInSmoothScrolling( JViewport viewport, boole
 		viewport.putClientProperty( clientPropertyName , isInSmoothScrolling? Boolean.TRUE: null);
 	}
 
-	private static List<JViewport> viewportList = new ArrayList<>();
+	private static Set<JViewport> viewportSet = Collections.newSetFromMap(new IdentityHashMap<JViewport, Boolean>());
 
 	public static synchronized void registerViewport( JViewport viewport ) {
 		if( instance == null )
 			return;
 		if(viewport.getParent() instanceof JScrollPane) {
-			viewportList.add( viewport );
+			viewportSet.add( viewport );
 		}
 	}
 
@@ -187,7 +188,7 @@ public static synchronized void unregisterViewport( JViewport viewport ) {
 		if( instance.isBlitScrollModeBlocked ) {
 			instance.setBlitScrollModeBlocked( viewport, false );
 		}
-		viewportList.remove( viewport );
+		viewportSet.remove( viewport );
 	}
 
 }