为什么会一直提示java.io.NotSerializableException: imooc.playlist.PlayList错误呢？

Question

PlayList类和Song类都已经继承了序列化接口啊：

    public class PlayList implements Serializable

    public class Song implements Serializable

主程序中的代码：

case 8:

System.out.println("导出歌单 ");

System.out.println("请输入要导出的歌曲列表名称： ");

instr = scanner.next();

String fileName = instr + "的歌单.txt";

if (playListCollection.searchPlayListByName(instr) != null) {

PlayList sPlayList = playListCollection.searchPlayListByName(instr);

try {

FileOutputStream fos = new FileOutputStream(fileName);

ObjectOutputStream oos = new ObjectOutputStream(fos);

FileInputStream fis = new FileInputStream(fileName);

ObjectInputStream ois = new ObjectInputStream(fis);

// 写入对象

// oos.writeObject(sPlayList);

Iterator<Song> it = sPlayList.getMusicList().iterator();

while (it.hasNext()) {

oos.writeObject(it.next());

}

oos.flush();

// 读对象信息

try {

PlayList rPlayList = (PlayList) ois.readObject();

System.out.println(rPlayList);

} catch (ClassNotFoundException e) {

e.printStackTrace();

}

oos.close();

fos.close();

ois.close();

fis.close();

} catch (FileNotFoundException e) {

e.printStackTrace();

} catch (IOException e) {

e.printStackTrace();

}

}

PlayListMenu();

break;