以编程方式阻止应用程序

Question

我在StackOverflow上找到了答案，但我遇到了一些困难。我有以下代码：

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    PackageManager packageManager = getPackageManager();
    Intent mainIntent = new Intent(Intent.ACTION_MAIN);
    mainIntent.addCategory(Intent.CATEGORY_LAUNCHER);
    List<ResolveInfo> appList = packageManager.queryIntentActivities(mainIntent,0);
    Collections.sort(appList, new ResolveInfo.DisplayNameComparator(packageManager));
    List<PackageInfo> packs = packageManager.getInstalledPackages(0);
    for (int i=0; i<packs.size();i++){
        PackageInfo p = packs.get(i);
        ApplicationInfo a = p.applicationInfo;

        if((a.flags & ApplicationInfo.FLAG_SYSTEM)==1){
            continue;
        }
        apps.add(p.packageName);

        ActivityManager mActivityManager =(ActivityManager) getSystemService(Context.ACTIVITY_SERVICE);
        List<ActivityManager.RunningTaskInfo> RunningTask = mActivityManager.getRunningTasks(1);
        ActivityManager.RunningTaskInfo ar = RunningTask.get(0);
        activityOnTop = ar.topActivity.getClassName();
        Context mContext = getApplicationContext();
        Intent lockIntent = new Intent(mContext, LockScreen.class);
        lockIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        mContext.startActivity(lockIntent);

        Intent startHomescreen = new Intent(Intent.ACTION_MAIN);
        startHomescreen.addCategory(Intent.CATEGORY_HOME);
        startHomescreen.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);
        startActivity(startHomescreen);
    }

我遇到困难的地方是android工作室说apps中的apps.add(p.packageName);未定义，activityOnTop中的activityOnTop = ar.topActivity.getClassName();也未定义。最后，lockscreen中的Intent lockIntent = new Intent(mContext, LockScreen.class);未定义任何人都可以帮助我解决这些问题吗？请记住，这是onCreate方法的全部内容，我应该将它移到另一个类吗？