file 外部存储

public class MainActivity extends AppCompatActivity {

private static final String TAG = "MainActivity";
ArrayList<Person> persons;
ArrayAdapter<Person> arrayAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    persons = new ArrayList<>();
    restore();

    ListView listView = findViewById(R.id.listView);
    arrayAdapter = new ArrayAdapter<Person>(this,android.R.layout.simple_list_item_1,persons);
    listView.setAdapter(arrayAdapter);

//
// if (ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED){
// ActivityCompat.requestPermissions(this,new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},0);
// }
}

public void add(View v){
    EditText editText_name = findViewById(R.id.editText_name);
    EditText editText_age = findViewById(R.id.editText_age);

    Person person = new Person(editText_name.getText().toString(),Integer.parseInt(editText_age.getText().toString()));
    persons.add(person);
    arrayAdapter.notifyDataSetChanged();

}

@Override
protected void onPause() {
    super.onPause();
    save();
}

//外部存储
public void save(){
    try {

// File file = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS);
File file = getExternalFilesDir(Environment.DIRECTORY_DOWNLOADS);
Log.d(TAG, "save: "+file.getAbsolutePath());
FileOutputStream fileOutputStream = new FileOutputStream(file.getAbsolutePath()+"/persons");
// FileOutputStream fileOutputStream = openFileOutput("persons",MODE_PRIVATE);
ObjectOutputStream objectOutputStream = new ObjectOutputStream(fileOutputStream);

        objectOutputStream.writeObject(persons);

        objectOutputStream.close();
        fileOutputStream.close();

    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

public void restore(){
    try {

// File file = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS);
File file = getExternalFilesDir(Environment.DIRECTORY_DOWNLOADS);
FileInputStream fileInputStream = new FileInputStream(file.getAbsolutePath()+"/persons");

// FileInputStream fileInputStream = openFileInput("persons");
ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream);

        persons = (ArrayList<Person>) objectInputStream.readObject();

        fileInputStream.close();
        objectInputStream.close();

    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    }
}

// public void save(){
// try {
// FileOutputStream fileOutputStream = openFileOutput("persons",MODE_PRIVATE);
// ObjectOutputStream objectOutputStream = new ObjectOutputStream(fileOutputStream);
//
// objectOutputStream.writeObject(persons);
//
// objectOutputStream.close();
// fileOutputStream.close();
//
// } catch (FileNotFoundException e) {
// e.printStackTrace();
// } catch (IOException e) {
// e.printStackTrace();
// }
// }
//
// public void restore(){
// try {
// FileInputStream fileInputStream = openFileInput("persons");
// ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream);
//
// persons = (ArrayList<Person>) objectInputStream.readObject();
//
// fileInputStream.close();
// objectInputStream.close();
//
// } catch (FileNotFoundException e) {
// e.printStackTrace();
// } catch (IOException e) {
// e.printStackTrace();
// } catch (ClassNotFoundException e) {
// e.printStackTrace();
// }
// }
}

package cn.edu.sicnu.persondemo;

import java.io.Serializable;

/**

• Created by liguiyang on 2018/4/24.
  */

public class Person implements Serializable {
String name;
int age;

public Person(String name, int age) {
    this.name = name;
    this.age = age;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public int getAge() {
    return age;
}

public void setAge(int age) {
    this.age = age;
}

@Override
public String toString() {
    return "Person{" +
            "name='" + name + '\'' +
            ", age=" + age +
            '}';
}

}