关于openFileOutput无法创建文件

在小米4和魅族pro5上都试过，还是看不到创建的文件

                                            String FILENAME = "hello_file";
                    String string = "hello world!";
                    try{
                        FileOutputStream fos = openFileOutput(FILENAME, Context.MODE_PRIVATE);
                        try{
                            fos.write(string.getBytes());
                            fos.flush();
                            fos.close();
                        } catch (IOException e) {
                            Log.e("TextActivity:", "IOException");
                            e.printStackTrace();
                        }

                    } catch (FileNotFoundException e) {
                        Log.e("TextActivity:", "FileNotFound");
                        e.printStackTrace();
                    }