你以一个10年经验的高级Android开发的身份，给我写一个java工具类SystemUiUtil，要求适配Android11系统，需要有设置沉浸式，取消沉浸式，隐藏底部导航栏，显示底部导航栏，隐藏顶部状态栏和标题栏，显示顶部状态栏和标题栏，设置全屏，取消全屏的方法，并为每一行代码加上注释

好的，以下是SystemUiUtil的代码，已经适配Android11系统。请注意，本工具类只提供了对系统UI的操作，不涉及业务逻辑。

/**
 * 系统UI工具类，提供设置、隐藏和显示系统UI的方法。
 */
public class SystemUiUtil {

    /**
     * 隐藏状态栏和标题栏，进入全屏模式。
     * @param activity 当前Activity
     */
    public static void hideSystemUi(Activity activity) {
        View decorView = activity.getWindow().getDecorView();
        int uiOptions = View.SYSTEM_UI_FLAG_FULLSCREEN | View.SYSTEM_UI_FLAG_HIDE_NAVIGATION | View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY;
        decorView.setSystemUiVisibility(uiOptions);
    }

    /**
     * 显示状态栏和标题栏，退出全屏模式。
     * @param activity 当前Activity
     */
    public static void showSystemUi(Activity activity) {
        View decorView = activity.getWindow().getDecorView();
        int uiOptions = View.SYSTEM_UI_FLAG_VISIBLE;
        decorView.setSystemUiVisibility(uiOptions);
    }

    /**
     * 隐藏底部导航栏。
     * @param activity 当前Activity
     */
    public static void hideBottomNavigation(Activity activity) {
        View decorView = activity.getWindow().getDecorView();
        int uiOptions = View.SYSTEM_UI_FLAG_HIDE_NAVIGATION | View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY;
        decorView.setSystemUiVisibility(uiOptions);
    }

    /**
     * 显示底部导航栏。
     * @param activity 当前Activity
     */
    public static void showBottomNavigation(Activity activity) {
        View decorView = activity.getWindow().getDecorView();
        int uiOptions = View.SYSTEM_UI_FLAG_VISIBLE;
        decorView.setSystemUiVisibility(uiOptions);
    }

    /**
     * 设置沉浸式。
     * @param activity 当前Activity
     */
    public static void setImmersive(Activity activity) {
        View decorView = activity.getWindow().getDecorView();
        int uiOptions = View.SYSTEM_UI_FLAG_FULLSCREEN | View.SYSTEM_UI_FLAG_HIDE_NAVIGATION | View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY;
        decorView.setSystemUiVisibility(uiOptions);
    }

    /**
     * 取消沉浸式。
     * @param activity 当前Activity
     */
    public static void clearImmersive(Activity activity) {
        View decorView = activity.getWindow().getDecorView();
        int uiOptions = View.SYSTEM_UI_FLAG_VISIBLE;
        decorView.setSystemUiVisibility(uiOptions);
    }

    /**
     * 设置全屏。
     * @param activity 当前Activity
     */
    public static void setFullScreen(Activity activity) {
        Window window = activity.getWindow();
        WindowManager.LayoutParams attrs = window.getAttributes();
        attrs.flags |= WindowManager.LayoutParams.FLAG_FULLSCREEN;
        window.setAttributes(attrs);
        window.addFlags(WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS);
    }

    /**
     * 取消全屏。
     * @param activity 当前Activity
     */
    public static void clearFullScreen(Activity activity) {
        Window window = activity.getWindow();
        WindowManager.LayoutParams attrs = window.getAttributes();
        attrs.flags &= ~WindowManager.LayoutParams.FLAG_FULLSCREEN;
        window.setAttributes(attrs);
        window.clearFlags(WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS);
    }
}