java - 内部ストレージを使用してカスタム オブジェクトの ArrayList を保存する方法は?

Question

内部ストレージを使用して、WordList というカスタム オブジェクトの ArrayList を格納したいと考えています。

これが私のコードです：

@SuppressWarnings("serial")
public class WordList extends MainActivity implements Serializable {

public String name;
public ArrayList<String> wordarray;
public ArrayList<String> definitionarray;

public WordList(String newName)
{
    this.name = newName;
    this.wordarray = new ArrayList<String>();
    this.definitionarray = new ArrayList<String>();
}

public String getName()
{
    return name;
}

private void writeObject(ObjectOutputStream out) throws IOException {
    out.writeUTF(name);
    out.writeObject(wordarray);
    out.writeObject(definitionarray);
}

private void readObject(ObjectInputStream in) throws IOException,
        ClassNotFoundException {
    name = in.readUTF();
    wordarray = (ArrayList<String>) in.readObject();
    definitionarray = (ArrayList<String>) in.readObject();
}  
}

そして、主な活動は次のとおりです。

    public class MainActivity extends Activity {
private EditText text;
private ArrayList<WordList> lists = new ArrayList<WordList>();
private TextView textview;
FileOutputStream fos;
String filePath;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    text = (EditText) findViewById(R.id.editText1);
    textview = (TextView) findViewById(R.id.test);
    filePath = getApplicationContext().getFilesDir().getPath().toString() + ".fileName.txt";
}


public void onClick(View view) throws FileNotFoundException {
    switch (view.getId()) {
    case R.id.addtoarray:
        String input = text.getText().toString();
        WordList list = new WordList(input);
        lists.add(list);
        break;
    case R.id.save:
        try {
            File f = new File(filePath);
            FileOutputStream fos = new FileOutputStream(f, true);
            ObjectOutputStream oos = new ObjectOutputStream(fos);
            Toast.makeText(getApplicationContext(), "Wrote " + String.valueOf(lists.size() + "objects to file!"), Toast.LENGTH_LONG).show();
            oos.writeInt(lists.size());
            for(int i=0; i<lists.size(); i++)
            {
                oos.writeObject(lists.get(i));
            }
            oos.close();
            fos.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        break;
    case R.id.load:
        File saveFile = new File(filePath);
        if (saveFile.exists())
        {
            Toast.makeText(getApplicationContext(), "File found!",
                    Toast.LENGTH_SHORT).show(); 
        try {
            FileInputStream fis = new FileInputStream(saveFile);
            ObjectInputStream ois = new ObjectInputStream(fis);
            int num = ois.readInt();
            for(int i = 0; i<num; i++)
            {
                WordList o = (WordList) ois.readObject();
                lists.add(o);
            }
            fis.close();
            ois.close();
        } catch (FileNotFoundException e) {
          e.printStackTrace();
      } catch (StreamCorruptedException e) {
          e.printStackTrace();
      } catch (IOException e) {
          e.printStackTrace();
      } catch (ClassNotFoundException e) {
          e.printStackTrace();
      }
    } else {
        Toast.makeText(getApplicationContext(), "File not found!",
              Toast.LENGTH_SHORT).show();
    }
        textview.setText(lists.get(0).getName());
        break;
    }
}

Toasts に関しては、オブジェクトは保存されますが、アプリでの読み取りに問題があります。誰かが私がここで間違っていることを教えてもらえますか?