no longer use static fields for shared instances of UI delegates because this makes problems in GUI builders that support Laf switching and use more than one FlatLaf theme at the same time

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

@@ -700,6 +700,18 @@ public abstract class FlatLaf
 		MnemonicHandler.showMnemonics( false, null );
 	}
 
+	// do not allow overriding to avoid issues in FlatUIUtils.createSharedUI()
+	@Override
+	public final boolean equals( Object obj ) {
+		return super.equals( obj );
+	}
+
+	// do not allow overriding to avoid issues in FlatUIUtils.createSharedUI()
+	@Override
+	public final int hashCode() {
+		return super.hashCode();
+	}
+
 	//---- class ActiveFont ---------------------------------------------------
 
 	private static class ActiveFont

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

@@ -132,12 +132,8 @@ public class FlatButtonUI
 
 	private boolean defaults_initialized = false;
 
-	private static ComponentUI instance;
-
 	public static ComponentUI createUI( JComponent c ) {
-		if( instance == null )
+		return FlatUIUtils.createSharedUI( FlatButtonUI.class, FlatButtonUI::new );
-			instance = new FlatButtonUI();
-		return instance;
 	}
 
 	@Override

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

@@ -42,12 +42,8 @@ import javax.swing.plaf.ComponentUI;
 public class FlatCheckBoxUI
 	extends FlatRadioButtonUI
 {
-	private static ComponentUI instance;
-
 	public static ComponentUI createUI( JComponent c ) {
-		if( instance == null )
+		return FlatUIUtils.createSharedUI( FlatCheckBoxUI.class, FlatCheckBoxUI::new );
-			instance = new FlatCheckBoxUI();
-		return instance;
 	}
 
 	@Override

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

@@ -56,12 +56,8 @@ public class FlatLabelUI
 
 	private boolean defaults_initialized = false;
 
-	private static ComponentUI instance;
-
 	public static ComponentUI createUI( JComponent c ) {
-		if( instance == null )
+		return FlatUIUtils.createSharedUI( FlatLabelUI.class, FlatLabelUI::new );
-			instance = new FlatLabelUI();
-		return instance;
 	}
 
 	@Override

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

@@ -35,11 +35,7 @@ import javax.swing.plaf.basic.BasicPanelUI;
 public class FlatPanelUI
 	extends BasicPanelUI
 {
-	private static ComponentUI instance;
-
 	public static ComponentUI createUI( JComponent c ) {
-		if( instance == null )
+		return FlatUIUtils.createSharedUI( FlatPanelUI.class, FlatPanelUI::new );
-			instance = new FlatPanelUI();
-		return instance;
 	}
 }

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

@@ -38,12 +38,8 @@ import javax.swing.plaf.ComponentUI;
 public class FlatPopupMenuSeparatorUI
 	extends FlatSeparatorUI
 {
-	private static ComponentUI instance;
-
 	public static ComponentUI createUI( JComponent c ) {
-		if( instance == null )
+		return FlatUIUtils.createSharedUI( FlatPopupMenuSeparatorUI.class, FlatPopupMenuSeparatorUI::new );
-			instance = new FlatPopupMenuSeparatorUI();
-		return instance;
 	}
 
 	@Override

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

@@ -60,12 +60,8 @@ public class FlatRadioButtonUI
 
 	private boolean defaults_initialized = false;
 
-	private static ComponentUI instance;
-
 	public static ComponentUI createUI( JComponent c ) {
-		if( instance == null )
+		return FlatUIUtils.createSharedUI( FlatRadioButtonUI.class, FlatRadioButtonUI::new );
-			instance = new FlatRadioButtonUI();
-		return instance;
 	}
 
 	@Override

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

@@ -52,12 +52,8 @@ public class FlatSeparatorUI
 
 	private boolean defaults_initialized = false;
 
-	private static ComponentUI instance;
-
 	public static ComponentUI createUI( JComponent c ) {
-		if( instance == null )
+		return FlatUIUtils.createSharedUI( FlatSeparatorUI.class, FlatSeparatorUI::new );
-			instance = new FlatSeparatorUI();
-		return instance;
 	}
 
 	@Override

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

@@ -82,12 +82,8 @@ public class FlatToggleButtonUI
 
 	private boolean defaults_initialized = false;
 
-	private static ComponentUI instance;
-
 	public static ComponentUI createUI( JComponent c ) {
-		if( instance == null )
+		return FlatUIUtils.createSharedUI( FlatToggleButtonUI.class, FlatToggleButtonUI::new );
-			instance = new FlatToggleButtonUI();
-		return instance;
 	}
 
 	@Override

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

@@ -50,12 +50,8 @@ public class FlatToolBarSeparatorUI
 
 	private boolean defaults_initialized = false;
 
-	private static ComponentUI instance;
-
 	public static ComponentUI createUI( JComponent c ) {
-		if( instance == null )
+		return FlatUIUtils.createSharedUI( FlatToolBarSeparatorUI.class, FlatToolBarSeparatorUI::new );
-			instance = new FlatToolBarSeparatorUI();
-		return instance;
 	}
 
 	@Override

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

@@ -52,12 +52,8 @@ public class FlatToolTipUI
 {
 	private static PropertyChangeListener sharedPropertyChangedListener;
 
-	private static ComponentUI instance;
-
 	public static ComponentUI createUI( JComponent c ) {
-		if( instance == null )
+		return FlatUIUtils.createSharedUI( FlatToolTipUI.class, FlatToolTipUI::new );
-			instance = new FlatToolTipUI();
-		return instance;
 	}
 
 	@Override

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

@@ -35,7 +35,10 @@ import java.awt.event.MouseEvent;
 import java.awt.geom.Path2D;
 import java.awt.geom.Rectangle2D;
 import java.awt.geom.RoundRectangle2D;
+import java.util.IdentityHashMap;
+import java.util.WeakHashMap;
 import java.util.function.Consumer;
+import java.util.function.Supplier;
 import javax.swing.JComponent;
 import javax.swing.JTable;
 import javax.swing.LookAndFeel;
@@ -43,6 +46,7 @@ import javax.swing.SwingUtilities;
 import javax.swing.UIManager;
 import javax.swing.border.Border;
 import javax.swing.border.CompoundBorder;
+import javax.swing.plaf.ComponentUI;
 import javax.swing.plaf.UIResource;
 import com.formdev.flatlaf.FlatClientProperties;
 import com.formdev.flatlaf.util.DerivedColor;
@@ -59,6 +63,8 @@ public class FlatUIUtils
 {
 	public static final boolean MAC_USE_QUARTZ = Boolean.getBoolean( "apple.awt.graphics.UseQuartz" );
 
+	private static WeakHashMap<LookAndFeel, IdentityHashMap<Object, ComponentUI>> sharedUIinstances = new WeakHashMap<>();
+
 	public static Rectangle addInsets( Rectangle r, Insets insets ) {
 		return new Rectangle(
 			r.x - insets.left,
@@ -534,6 +540,19 @@ public class FlatUIUtils
 		return explicitlySet;
 	}
 
+	/**
+	 * Creates a shared component UI for the given key and the current Laf.
+	 * Each Laf instance has its own shared component UI instance.
+	 * <p>
+	 * This is for GUI builders that support Laf switching and
+	 * may use multiple Laf instances at the same time.
+	 */
+	public static ComponentUI createSharedUI( Object key, Supplier<ComponentUI> newInstanceSupplier ) {
+		return sharedUIinstances
+			.computeIfAbsent( UIManager.getLookAndFeel(), k -> new IdentityHashMap<>() )
+			.computeIfAbsent( key, k -> newInstanceSupplier.get() );
+	}
+
 	//---- class HoverListener ------------------------------------------------
 
 	public static class HoverListener

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

@@ -38,12 +38,8 @@ import javax.swing.plaf.basic.BasicViewportUI;
 public class FlatViewportUI
 	extends BasicViewportUI
 {
-	private static ComponentUI instance;
-
 	public static ComponentUI createUI( JComponent c ) {
-		if( instance == null )
+		return FlatUIUtils.createSharedUI( FlatViewportUI.class, FlatViewportUI::new );
-			instance = new FlatViewportUI();
-		return instance;
 	}
 
 	@Override