(feature) extend flat inspector

flatlaf-extras/src/main/java/com/formdev/flatlaf/extras/FlatInspector.java

@@ -554,12 +554,16 @@ else if( c instanceof JToolBar )
 		appendRow( buf, "Left-to-right", String.valueOf( c.getComponentOrientation().isLeftToRight() ) );
 		appendRow( buf, "Parent", (c.getParent() != null ? toString( c.getParent().getClass(), classHierarchy ) : "null") );
 
-		if( c instanceof JComponent ) {
+	if( c instanceof JComponent ) {
 			Object style = ((JComponent)c).getClientProperty( FlatClientProperties.STYLE );
 			if( style != null )
 				appendRow( buf, "FlatLaf Style", style.toString() );
 		}
 
+		if( c instanceof FlatInspectorInfoProvider ) {
+			((FlatInspectorInfoProvider) c).appendInspectorInfo( buf, classHierarchy );
+		}
+
 		// append parent level
 		buf.append( "<tr><td colspan=\"2\">" );
 		if( parentLevel > 0 )
@@ -582,15 +586,15 @@ else if( c instanceof JToolBar )
 		return buf.toString();
 	}
 
-	private static void appendRow( StringBuilder buf, String key, String value ) {
+	public static void appendRow( StringBuilder buf, String key, String value ) {
 		buf.append( "<tr><td valign=\"top\">" )
 			.append( key )
 			.append( ":</td><td>" )
 			.append( value )
 			.append( "</td></tr>" );
 	}
 
-	private static String toString( Class<?> cls, boolean classHierarchy ) {
+	public static String toString( Class<?> cls, boolean classHierarchy ) {
 		StringBuilder buf = new StringBuilder( 100 );
 		int level = 0;
 
@@ -623,15 +627,15 @@ private static String toString( Class<?> cls, boolean classHierarchy ) {
 		return buf.toString();
 	}
 
-	private static String toString( Insets insets ) {
+	public static String toString( Insets insets ) {
 		if( insets == null )
 			return "null";
 
 		return insets.top + ", " + insets.left + ", " + insets.bottom + ", " + insets.right
 			+ (insets instanceof UIResource ? " UI" : "");
 	}
 
-	private static String toString( Color c ) {
+	public static String toString( Color c ) {
 		if( c == null )
 			return "null";
 
@@ -660,15 +664,15 @@ private static String toString( Color c ) {
 		return buf.toString();
 	}
 
-	private static String toString( Font f ) {
+	public static String toString( Font f ) {
 		if( f == null )
 			return "null";
 
 		return f.getFamily() + " " + f.getSize() + " " + f.getStyle()
 			+ (f instanceof UIResource ? " UI" : "");
 	}
 
-	private static String toString( Border b, boolean classHierarchy ) {
+	public static String toString( Border b, boolean classHierarchy ) {
 		if( b == null )
 			return "null";
 

flatlaf-extras/src/main/java/com/formdev/flatlaf/extras/FlatInspectorInfoProvider.java

@@ -0,0 +1,52 @@
+/*
+ * Copyright 2026 FormDev Software GmbH
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.formdev.flatlaf.extras;
+
+/**
+ * Implement this interface in a {@link java.awt.Component} to let {@link FlatInspector}
+ * show additional, component-specific information in its debug tooltip.
+ * <p>
+ * {@link #appendInspectorInfo(StringBuilder,boolean)} is invoked while
+ * {@code FlatInspector} is building the HTML tooltip content for the inspected component.
+ * The rows are appended after the built-in "FlatLaf Style" row and before the footer
+ * that shows the parent inspection level and key bindings hint.
+ */
+public interface FlatInspectorInfoProvider
+{
+	/**
+	 * Appends additional HTML table rows with component-specific debug information.
+	 * <p>
+	 * Use {@link FlatInspector#appendRow(StringBuilder, String, String)} to append rows,
+	 * and the {@code FlatInspector.toString(...)} helpers (for {@link Class},
+	 * {@link java.awt.Insets}, {@link java.awt.Color}, {@link java.awt.Font},
+	 * {@link javax.swing.border.Border}) to format values the same way the rest of the
+	 * tooltip does, e.g.:
+	 * <pre>
+	 * FlatInspector.appendRow( buf, "Model",
+	 *     FlatInspector.toString( model.getClass(), showClassHierarchy ) );
+	 * </pre>
+	 * Values are inserted as-is (not HTML-escaped), so avoid passing raw user text that
+	 * may contain {@code <}, {@code >} or {@code &} unless it is already safe to embed
+	 * as HTML.
+	 *
+	 * @param buf the buffer used to build the tooltip HTML
+	 * @param showClassHierarchy whether the user has toggled display of the full class
+	 *        hierarchy (Alt key); pass this through to
+	 *        {@code FlatInspector.toString(Class, boolean)} calls for consistency
+	 */
+	void appendInspectorInfo( StringBuilder buf, boolean showClassHierarchy );
+}