• 1. Serializable

流程：

• 1. 带数据的类implements Serializable，子类也要，如下，getter和setter自己加

public class Student implements Serializable {
    private String name;
    private transient int age; // 不序列化保存的用transient
    private Score score;
}

class Score implements Serializable{
    private int math;
    private String grade;
}

• 2. 输出到文件

            ObjectOutputStream objectOutputStream = new ObjectOutputStream(openFileOutput(FILE_NAME, MODE_PRIVATE));//覆盖
            objectOutputStream.writeObject(student);
            objectOutputStream.flush(); // 清空缓存
            objectOutputStream.close();

• 3. 读取：

                ObjectInputStream objectInputStream = new ObjectInputStream(openFileInput(FILE_NAME));
                Student student1 = (Student) objectInputStream.readObject();

• 4. 关于 transient:
     测试1：transient int型，读取后输出结果为0
     测试2：transient Object型，可读取，输出报错，因为Object为null
     测试3：transient String，可读取，输出为null

• 注意事项
  该接口会自动定义一个long型版本号，若数据结构发生改变，则以前保存的数据读取不出来，解决方法：人为添加版本号：

  
  
  
  

  然后没加版本号的类会标黄，alt+Enter自动加：

    private static final long serialVersionUID = -392086972009226958L;

• Parcelable

1. 添加implements Parcelable

2. 生成 (点类名：顺序不要动

   
   

3. 使用：例如在activity传递

                Intent intent = new Intent(MainActivity.this,DetailActivity.class);
                Bundle bundle = new Bundle();
                bundle.putParcelable("studentObject", student);
                intent.putExtra("data", bundle);
                startActivity(intent);

4. 获取：

        Intent intent = getIntent();
        Bundle bundle = intent.getBundleExtra("data");
        Student student =  bundle.getParcelable("studentObject");
        binding.textView2.setText(student.getName()); // 显示

• Json

测试工具：

code - reformat code
转换例子，类和json对应就好，基础教程网上很多，不写了：

        final Student student = new Student("name",18,new Score(98,"a"));
        Gson gson = new Gson();
        String str = gson.toJson(student);
        String str1 = "{\"name\":\"name\",\"score\":{\"grade\":\"a\",\"math\":98}}";
        Student student1 = gson.fromJson(str1, Student.class);

支持列表：

        final Student student = new Student("name",18,new Score(98,"a"));
        final Student student1 = new Student("name1",181,new Score(981,"a1"));
        Student[] students = {student,student1};
        Gson gson = new Gson();
        String result = gson.toJson(students);

列表内为方括号

反序列化：

        Student[] students1 = gson.fromJson(str1, Student[].class);
        List<Student> list = Arrays.asList(students1);

或者list，结果和数组一样：

        final Student student = new Student("name",18,new Score(98,"a"));
        final Student student1 = new Student("name1",181,new Score(981,"a1"));
        List<Student> studentList = new ArrayList<>();
        studentList.add(student);
        studentList.add(student1);
        Gson gson = new Gson();
        String str = gson.toJson(studentList);

• 注意，不能直接强制用List.class反序列到list，会出问题
  需要定义一个Type：

        Type typeStudent = new TypeToken<List<Student>>(){}.getType();
        List<Student> studentList = new ArrayList<>();
        studentList = gson.fromJson(str1,typeStudent);

• 定义封装名字：

public class Student{
    @SerializedName("student_name")
    private String name;

这样出来的就是

  {
    "student_name": "name",
    "score": {
      "grade": "a",
      "math": 98
    }