static String resolveValueFromUIManager( String value )
		throws IllegalArgumentException
	{
		if( value.startsWith( VARIABLE_PREFIX ) ) {
			@SuppressWarnings( "unchecked" )
			Map<String, String> variables = (Map<String, String>) UIManager.get( KEY_VARIABLES );
			String newValue = (variables != null) ? variables.get( value ) : null;
			if( newValue == null )
				throw new IllegalArgumentException( "variable '" + value + "' not found" );

			return resolveValueFromUIManager( newValue );
		}

		if( !value.startsWith( PROPERTY_PREFIX ) )
			return value;

		String key = value.substring( PROPERTY_PREFIX.length() );
		Object newValue = UIManager.get( key );
		if( newValue == null )
			throw new IllegalArgumentException( "property '" + key + "' not found" );

		// convert binary color to string
		if( newValue instanceof Color ) {
			Color color = (Color) newValue;
			int rgb = color.getRGB() & 0xffffff;
			int alpha = color.getAlpha();
			return (alpha != 255)
				? String.format( "#%06x%02x", rgb, alpha )
				: String.format( "#%06x", rgb );
		}

		throw new IllegalArgumentException( "property value type '" + newValue.getClass().getName() + "' not supported in references" );
	}
Similar to Class.getSimpleName(), but includes enclosing class for nested classes.
flatlaf-core/src/main/java/com/formdev/flatlaf/UIDefaultsLoader.java