FileOutputStream中和寫入方法

伊馬初學者在機器人......我想知道爲什麼在我的代碼FOS成爲空這裏是我的主要activity.java文件FileOutputStream中和寫入方法

public class MainActivity extends AppCompatActivity { 

@RequiresApi(api = Build.VERSION_CODES.M) 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    FileOutputStream fos = null; 
    TextView tv = (TextView) findViewById(R.id.tv); 
    if (checkSelfPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED) { 
     try { 
      File root = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DCIM); 
      File dir = new File(root.getAbsolutePath() + "/musics"); 
      dir.mkdir(); 
      File file = new File(dir, "myData.txt"); 
      fos = new FileOutputStream(file); 
     } catch (FileNotFoundException e) { 
      e.printStackTrace(); 
     } 
     try { 
      fos.write("good morning".getBytes()); 
     } catch (IOException e) { 
      e.printStackTrace(); 
     } finally { 
      if (fos != null) { 
       try { 
        fos.close(); 
       } catch (IOException e) { 
        e.printStackTrace(); 
       } 
      } else { 
       Log.e("fos", "null"); 
      } 
     } 
    } else { 
     Toast.makeText(MainActivity.this, "permission not granted", Toast.LENGTH_LONG).show(); 
     requestPermissions(new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, 101); 
    } 
    tv.setText(fos + ""); 
} 
@Override 
public void onRequestPermissionsResult(int requestCode,String[] permissions,int[] grantResults) { 
    FileOutputStream fos = null; 
    if (requestCode == 101 && grantResults[0] == PackageManager.PERMISSION_GRANTED) { 
     try { 
      File root = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DCIM); 
      File dir = new File(root.getAbsolutePath() + "/musics"); 
      dir.mkdir(); 
      File file = new File(dir, "myData.txt"); 
      fos = new FileOutputStream(file); 
     } catch (FileNotFoundException e) { 
      e.printStackTrace(); 
     } 
     try { 
      fos.write("good morning".getBytes()); 
     } catch (IOException e) { 
      e.printStackTrace(); 
     } finally { 
      if (fos != null) { 
       try { 
        fos.close(); 
       } catch (IOException e) { 
        e.printStackTrace(); 
       } 
      } else { 
       Log.e("fos", "null"); 
      } 
     } 
    } else { 
     super.onRequestPermissionsResult(requestCode, permissions, grantResults); 
    } 

}

，這裏是日誌味精