Improved subclassing:

- reviewed all private methods and made them protected/public where it might be useful for subclasses
- ComboBox and Spinner: added protected getBackground() and getForeground() methods to allow subclasses to change colors
- TabbedPane: moved tab separator painting to own method

(issue #113)

flatlaf-core/src/main/java/com/formdev/flatlaf/icons/FlatCheckBoxMenuItemIcon.java

@@ -67,14 +67,14 @@ public class FlatCheckBoxMenuItemIcon
 		g2.draw( path );
 	}
 
-	private Color getCheckmarkColor( Component c ) {
+	protected Color getCheckmarkColor( Component c ) {
 		if( c instanceof JMenuItem && ((JMenuItem)c).isArmed() && !isUnderlineSelection() )
 			return selectionForeground;
 
 		return c.isEnabled() ? checkmarkColor : disabledCheckmarkColor;
 	}
 
-	private boolean isUnderlineSelection() {
+	protected boolean isUnderlineSelection() {
 		// not storing value of "MenuItem.selectionType" in class to allow changing at runtime
 		return "underline".equals( UIManager.getString( "MenuItem.selectionType" ) );
 	}

flatlaf-core/src/main/java/com/formdev/flatlaf/icons/FlatMenuArrowIcon.java

@@ -65,14 +65,14 @@ public class FlatMenuArrowIcon
 		}
 	}
 
-	private Color getArrowColor( Component c ) {
+	protected Color getArrowColor( Component c ) {
 		if( c instanceof JMenu && ((JMenu)c).isSelected() && !isUnderlineSelection() )
 			return selectionForeground;
 
 		return c.isEnabled() ? arrowColor : disabledArrowColor;
 	}
 
-	private boolean isUnderlineSelection() {
+	protected boolean isUnderlineSelection() {
 		// not storing value of "MenuItem.selectionType" in class to allow changing at runtime
 		return "underline".equals( UIManager.getString( "MenuItem.selectionType" ) );
 	}

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

@@ -317,12 +317,11 @@ public class FlatComboBoxUI
 		// use non-UIResource colors because when SwingUtilities.updateComponentTreeUI()
 		// is used, then the editor is updated after the combobox and the
 		// colors are again replaced with default colors
-		boolean enabled = editor.isEnabled();
-		editor.setForeground( FlatUIUtils.nonUIResource( (enabled || editor instanceof JTextComponent)
-			? comboBox.getForeground()
-			: disabledForeground ) );
-		if( editor instanceof JTextComponent )
-			((JTextComponent)editor).setDisabledTextColor( FlatUIUtils.nonUIResource( disabledForeground ) );
+		boolean isTextComponent = editor instanceof JTextComponent;
+		editor.setForeground( FlatUIUtils.nonUIResource( getForeground( isTextComponent || editor.isEnabled() ) ) );
+
+		if( isTextComponent )
+			((JTextComponent)editor).setDisabledTextColor( FlatUIUtils.nonUIResource( getForeground( false ) ) );
 	}
 
 	@Override
@@ -358,9 +357,7 @@ public class FlatComboBoxUI
 		boolean isLeftToRight = comboBox.getComponentOrientation().isLeftToRight();
 
 		// paint background
-		g2.setColor( enabled
-			? (editableBackground != null && comboBox.isEditable() ? editableBackground : c.getBackground())
-			: getDisabledBackground( comboBox ) );
+		g2.setColor( getBackground( enabled ) );
 		FlatUIUtils.paintComponentBackground( g2, 0, 0, width, height, focusWidth, arc );
 
 		// paint arrow button background
@@ -399,8 +396,8 @@ public class FlatComboBoxUI
 		uninstallCellPaddingBorder( c );
 
 		boolean enabled = comboBox.isEnabled();
-		c.setForeground( enabled ? comboBox.getForeground() : disabledForeground );
-		c.setBackground( enabled ? comboBox.getBackground() : getDisabledBackground( comboBox ) );
+		c.setBackground( getBackground( enabled ) );
+		c.setForeground( getForeground( enabled ) );
 
 		boolean shouldValidate = (c instanceof JPanel);
 		if( padding != null )
@@ -420,8 +417,14 @@ public class FlatComboBoxUI
 		// not necessary because already painted in update()
 	}
 
-	private Color getDisabledBackground( JComponent c ) {
-		return isIntelliJTheme ? FlatUIUtils.getParentBackground( c ) : disabledBackground;
+	protected Color getBackground( boolean enabled ) {
+		return enabled
+			? (editableBackground != null && comboBox.isEditable() ? editableBackground : comboBox.getBackground())
+			: (isIntelliJTheme ? FlatUIUtils.getParentBackground( comboBox ) : disabledBackground);
+	}
+
+	protected Color getForeground( boolean enabled ) {
+		return enabled ? comboBox.getForeground() : disabledForeground;
 	}
 
 	@Override

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

@@ -371,7 +371,7 @@ debug*/
 		return menuItem instanceof JMenu && ((JMenu)menuItem).isTopLevelMenu();
 	}
 
-	private boolean isUnderlineSelection() {
+	protected boolean isUnderlineSelection() {
 		return "underline".equals( UIManager.getString( "MenuItem.selectionType" ) );
 	}
 
@@ -416,6 +416,13 @@ debug*/
 		if( accelerator == cachedAccelerator )
 			return cachedAcceleratorText;
 
+		cachedAccelerator = accelerator;
+		cachedAcceleratorText = getTextForAccelerator( accelerator );
+
+		return cachedAcceleratorText;
+	}
+
+	protected String getTextForAccelerator( KeyStroke accelerator ) {
 		StringBuilder buf = new StringBuilder();
 		int modifiers = accelerator.getModifiers();
 		if( modifiers != 0 )
@@ -427,10 +434,7 @@ debug*/
 		else
 			buf.append( accelerator.getKeyChar() );
 
-		cachedAccelerator = accelerator;
-		cachedAcceleratorText = buf.toString();
-
-		return cachedAcceleratorText;
+		return buf.toString();
 	}
 
 	//---- class MinSizeIcon --------------------------------------------------

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

@@ -240,7 +240,7 @@ public class FlatScrollBarUI
 		return button;
 	}
 
-	private boolean isShowButtons() {
+	protected boolean isShowButtons() {
 		Object showButtons = scrollbar.getClientProperty( FlatClientProperties.SCROLL_BAR_SHOW_BUTTONS );
 		if( showButtons == null && scrollbar.getParent() instanceof JScrollPane )
 			showButtons = ((JScrollPane)scrollbar.getParent()).getClientProperty( FlatClientProperties.SCROLL_BAR_SHOW_BUTTONS );

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

@@ -206,8 +206,8 @@ public class FlatSpinnerUI
 			// use non-UIResource colors because when SwingUtilities.updateComponentTreeUI()
 			// is used, then the text field is updated after the spinner and the
 			// colors are again replaced with default colors
-			textField.setForeground( FlatUIUtils.nonUIResource( spinner.getForeground() ) );
-			textField.setDisabledTextColor( FlatUIUtils.nonUIResource( disabledForeground ) );
+			textField.setForeground( FlatUIUtils.nonUIResource( getForeground( true ) ) );
+			textField.setDisabledTextColor( FlatUIUtils.nonUIResource( getForeground( false ) ) );
 		}
 	}
 
@@ -217,6 +217,16 @@ public class FlatSpinnerUI
 			: null;
 	}
 
+	protected Color getBackground( boolean enabled ) {
+		return enabled
+			? spinner.getBackground()
+			: (isIntelliJTheme ? FlatUIUtils.getParentBackground( spinner ) : disabledBackground);
+	}
+
+	protected Color getForeground( boolean enabled ) {
+		return enabled ? spinner.getForeground() : disabledForeground;
+	}
+
 	@Override
 	protected LayoutManager createLayout() {
 		return getHandler();
@@ -266,9 +276,7 @@ public class FlatSpinnerUI
 		boolean isLeftToRight = spinner.getComponentOrientation().isLeftToRight();
 
 		// paint background
-		g2.setColor( enabled
-			? c.getBackground()
-			: (isIntelliJTheme ? FlatUIUtils.getParentBackground( c ) : disabledBackground) );
+		g2.setColor( getBackground( enabled ) );
 		FlatUIUtils.paintComponentBackground( g2, 0, 0, width, height, focusWidth, arc );
 
 		// paint arrow buttons background

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

@@ -333,7 +333,13 @@ public class FlatTabbedPaneUI
 		// paint tab separators
 		if( clientPropertyBoolean( tabPane, TABBED_PANE_SHOW_TAB_SEPARATORS, showTabSeparators ) &&
 			!isLastInRun( tabIndex ) )
-		{
+		  paintTabSeparator( g, tabPlacement, x, y, w, h );
+
+		if( isSelected )
+			paintTabSelection( g, tabPlacement, x, y, w, h );
+	}
+
+	protected void paintTabSeparator( Graphics g, int tabPlacement, int x, int y, int w, int h ) {
 		float sepWidth = UIScale.scale( 1f );
 		float offset = tabSeparatorsFullHeight ? 0 : UIScale.scale( 5f );
 
@@ -350,10 +356,6 @@ public class FlatTabbedPaneUI
 		}
 	}
 
-		if( isSelected )
-			paintTabSelection( g, tabPlacement, x, y, w, h );
-	}
-
 	protected void paintTabSelection( Graphics g, int tabPlacement, int x, int y, int w, int h ) {
 		// increase clip bounds in scroll-tab-layout to paint over the separator line
 		Rectangle clipBounds = isScrollTabLayout() ? g.getClipBounds() : null;

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

@@ -86,7 +86,7 @@ public class FlatTableCellBorder
 		/**
 		 * Checks whether at least one selected cell is editable.
 		 */
-		private boolean isSelectionEditable( JTable table ) {
+		protected boolean isSelectionEditable( JTable table ) {
 			if( table.getRowSelectionAllowed() ) {
 				int columnCount = table.getColumnCount();
 				int[] selectedRows = table.getSelectedRows();

flatlaf-core/src/main/java/com/formdev/flatlaf/util/ColorFunctions.java

@@ -35,7 +35,7 @@ public class ColorFunctions
 		return HSLColor.toRGB( hsl, alpha );
 	}
 
-	private static float clamp( float value ) {
+	public static float clamp( float value ) {
 		return (value < 0)
 			? 0
 			: ((value > 100)

flatlaf-core/src/main/java/com/formdev/flatlaf/util/SystemInfo.java

@@ -68,7 +68,7 @@ public class SystemInfo
 		IS_KDE = (IS_LINUX && System.getenv( "KDE_FULL_SESSION" ) != null);
 	}
 
-	private static long scanVersion( String version ) {
+	public static long scanVersion( String version ) {
 		int major = 1;
 		int minor = 0;
 		int micro = 0;
@@ -86,7 +86,7 @@ public class SystemInfo
 		return toVersion( major, minor, micro, patch );
 	}
 
-	private static long toVersion( int major, int minor, int micro, int patch ) {
+	public static long toVersion( int major, int minor, int micro, int patch ) {
 		return ((long) major << 48) + ((long) minor << 32) + ((long) micro << 16) + patch;
 	}
 }