get UI defaults in shared instances only once (same as used in e.g. MetalRadioButtonUI)

Note: this optimization does not work when switching from one Flat LaF to another Flat LaF because UI uninstall/install is done per component

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

@@ -81,6 +81,8 @@ public class FlatButtonUI
 
 	private Icon helpButtonIcon;
 
+	private boolean defaults_initialized = false;
+
 	private static ComponentUI instance;
 
 	public static ComponentUI createUI( JComponent c ) {
@@ -93,6 +95,7 @@ public class FlatButtonUI
 	protected void installDefaults( AbstractButton b ) {
 		super.installDefaults( b );
 
+		if( !defaults_initialized ) {
 			String prefix = getPropertyPrefix();
 
 			focusWidth = UIManager.getInt( "Component.focusWidth" );
@@ -115,6 +118,9 @@ public class FlatButtonUI
 
 			helpButtonIcon = UIManager.getIcon( "HelpButton.icon" );
 
+			defaults_initialized = true;
+		}
+
 		MigLayoutVisualPadding.install( b, focusWidth );
 	}
 
@@ -123,6 +129,7 @@ public class FlatButtonUI
 		super.uninstallDefaults( b );
 
 		MigLayoutVisualPadding.uninstall( b );
+		defaults_initialized = false;
 	}
 
 	static boolean isContentAreaFilled( Component c ) {

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

@@ -39,6 +39,8 @@ public class FlatLabelUI
 {
 	private Color disabledForeground;
 
+	private boolean defaults_initialized = false;
+
 	private static ComponentUI instance;
 
 	public static ComponentUI createUI( JComponent c ) {
@@ -51,7 +53,17 @@ public class FlatLabelUI
 	protected void installDefaults( JLabel c ) {
 		super.installDefaults( c );
 
+		if( !defaults_initialized ) {
 			disabledForeground = UIManager.getColor( "Label.disabledForeground" );
+
+			defaults_initialized = true;
+		}
+	}
+
+	@Override
+	protected void uninstallDefaults( JLabel c ) {
+		super.uninstallDefaults( c );
+		defaults_initialized = false;
 	}
 
 	@Override

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

@@ -45,6 +45,8 @@ public class FlatSeparatorUI
 	protected int stripeWidth;
 	protected int stripeIndent;
 
+	private boolean defaults_initialized = false;
+
 	private static ComponentUI instance;
 
 	public static ComponentUI createUI( JComponent c ) {
@@ -57,10 +59,20 @@ public class FlatSeparatorUI
 	protected void installDefaults( JSeparator s ) {
 		super.installDefaults( s );
 
+		if( !defaults_initialized ) {
 			String prefix = getPropertyPrefix();
 			height = UIManager.getInt( prefix + ".height" );
 			stripeWidth = UIManager.getInt( prefix + ".stripeWidth" );
 			stripeIndent = UIManager.getInt( prefix + ".stripeIndent" );
+
+			defaults_initialized = true;
+		}
+	}
+
+	@Override
+	protected void uninstallDefaults( JSeparator s ) {
+		super.uninstallDefaults( s );
+		defaults_initialized = false;
 	}
 
 	protected String getPropertyPrefix() {

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

@@ -51,6 +51,8 @@ public class FlatToggleButtonUI
 
 	protected Color toolbarSelectedBackground;
 
+	private boolean defaults_initialized = false;
+
 	private static ComponentUI instance;
 
 	public static ComponentUI createUI( JComponent c ) {
@@ -68,11 +70,21 @@ public class FlatToggleButtonUI
 	protected void installDefaults( AbstractButton b ) {
 		super.installDefaults( b );
 
+		if( !defaults_initialized ) {
 			selectedBackground = UIManager.getColor( "ToggleButton.selectedBackground" );
 			selectedForeground = UIManager.getColor( "ToggleButton.selectedForeground" );
 			disabledSelectedBackground = UIManager.getColor( "ToggleButton.disabledSelectedBackground" );
 
 			toolbarSelectedBackground = UIManager.getColor( "ToggleButton.toolbar.selectedBackground" );
+
+			defaults_initialized = true;
+		}
+	}
+
+	@Override
+	protected void uninstallDefaults( AbstractButton b ) {
+		super.uninstallDefaults( b );
+		defaults_initialized = false;
 	}
 
 	@Override

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

@@ -46,6 +46,8 @@ public class FlatToolBarSeparatorUI
 	protected int separatorWidth;
 	protected Color separatorColor;
 
+	private boolean defaults_initialized = false;
+
 	private static ComponentUI instance;
 
 	public static ComponentUI createUI( JComponent c ) {
@@ -58,14 +60,24 @@ public class FlatToolBarSeparatorUI
 	protected void installDefaults( JSeparator c ) {
 		super.installDefaults( c );
 
+		if( !defaults_initialized ) {
 			separatorWidth = UIManager.getInt( "ToolBar.separatorWidth" );
 			separatorColor = UIManager.getColor( "ToolBar.separatorColor" );
 
+			defaults_initialized = true;
+		}
+
 		// necessary for vertical toolbars if separator size was set using setSeparatorSize()
 		// (otherwise there will be a gap on the left side of the vertical toolbar)
 		c.setAlignmentX( 0 );
 	}
 
+	@Override
+	protected void uninstallDefaults( JSeparator s ) {
+		super.uninstallDefaults( s );
+		defaults_initialized = false;
+	}
+
 	@Override
 	public Dimension getPreferredSize( JComponent c ) {
 		Dimension size = ((JToolBar.Separator)c).getSeparatorSize();