老师 这节课过时了，需要重新录制。

6.0是23，现在已经发布到27了。

所以按照步骤操作完毕一定会得到： (Permission denied)

07-20 17:04:13.813 28855-28923/com.example.netword_asynctask I/MainActivity: doInBackground: /storage/emulated/0/waqu.apk

07-20 17:04:13.815 28855-28923/com.example.netword_asynctask W/System.err: java.io.FileNotFoundException: /storage/emulated/0/waqu.apk (Permission denied)

        at java.io.FileOutputStream.open(Native Method)

        at java.io.FileOutputStream.<init>(FileOutputStream.java:221)

        at java.io.FileOutputStream.<init>(FileOutputStream.java:108)

        at com.example.netword_asynctask.MainActivity$DownloadAsyncTask.doInBackground(MainActivity.java:149)

        at com.example.netword_asynctask.MainActivity$DownloadAsyncTask.doInBackground(MainActivity.java:90)

        at android.os.AsyncTask$2.call(AsyncTask.java:304)