class PngConsumingTrayMenuController implements TrayMenuController {
    // ...
    public void updateTrayIcon(Consumer<TrayIconLoader> iconLoader) {
        TrayIconLoader.PngData callback = this::updateTrayIconWithPngData;
        iconLoader.accept(callback);
    }
    
    private void updateTrayIconWithPngData(byte[] data) {
        // ...
    }
    // ...
}

// with JEP 433:
updateTrayIcon(loader -> {
	switch (loader) {
		case TrayIconLoader.PngData l -> l.loadPng(new byte[0]);
		case TrayIconLoader.FreedesktopIconName l -> l.lookupByName("foo");
	}
});

// without JEP 433:
updateTrayIcon(loader -> {
	if (loader instanceof TrayIconLoader.PngData l) {
		l.loadPng(new byte[0]);
	} else if (loader instanceof TrayIconLoader.FreedesktopIconName l) {
		l.lookupByName("");
	}
});