SplitPane:

- update divider when client property `JSplitPane.expandableSide` changed
- Extras: added support for `JSplitPane.expandableSide` client property to `FlatSplitPane`

CHANGELOG.md

@@ -5,11 +5,16 @@ FlatLaf Change Log
 
 #### Fixed bugs
 
+- SplitPane: Update divider when client property `JSplitPane.expandableSide`
+  changed.
 - TabbedPane: Fixed swapped back and forward scroll buttons when using
   `TabbedPane.scrollButtonsPlacement = trailing` (regression in FlatLaf 3.3).
-- Extras: `FlatSVGIcon` color filters now support linear gradients. (PR #817)
 - Fixed missing window top border on Windows 10 in "full window content" mode.
   (issue 809)
+- Extras:
+  - `FlatSVGIcon` color filters now support linear gradients. (PR #817)
+  - Added support for `JSplitPane.expandableSide` client property to
+    `FlatSplitPane`.
 
 
 ## 3.4

flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatSplitPaneUI.java

@@ -301,6 +301,10 @@ public class FlatSplitPaneUI
 					// necessary to show/hide one-touch buttons on expand/collapse
 					doLayout();
 					break;
+
+				case FlatClientProperties.SPLIT_PANE_EXPANDABLE_SIDE:
+					revalidate();
+					break;
 			}
 		}
 

flatlaf-extras/src/main/java/com/formdev/flatlaf/extras/components/FlatSplitPane.java

@@ -16,6 +16,7 @@
 
 package com.formdev.flatlaf.extras.components;
 
+import static com.formdev.flatlaf.FlatClientProperties.*;
 import javax.swing.JSplitPane;
 
 /**
@@ -26,6 +27,29 @@ import javax.swing.JSplitPane;
  */
 public class FlatSplitPane
 	extends JSplitPane
-	implements FlatStyleableComponent
+	implements FlatComponentExtension, FlatStyleableComponent
 {
+	// NOTE: enum names must be equal to allowed strings
+	/** @since 3.4.1 */ public enum ExpandableSide { both, left, right }
+
+	/**
+	 * Returns what side of the spilt pane is allowed to expand
+	 * via one-touch expanding arrow buttons.
+	 *
+	 * @since 3.4.1
+	 */
+	public ExpandableSide getExpandableSide() {
+		return getClientPropertyEnumString( SPLIT_PANE_EXPANDABLE_SIDE, ExpandableSide.class,
+			null, ExpandableSide.both );
+	}
+
+	/**
+	 * Specifies what side of the spilt pane is allowed to expand
+	 * via one-touch expanding arrow buttons.
+	 *
+	 * @since 3.4.1
+	 */
+	public void setExpandableSide( ExpandableSide expandableSide ) {
+		putClientPropertyEnumString( SPLIT_PANE_EXPANDABLE_SIDE, expandableSide );
+	}
 }