文件存储的核心是Context提供了一个openFileOutput()与openFileInput()俩个方法

课程demo

public class MainActivity extends AppCompatActivity {
private EditText edit;
    private TextView tx;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        edit= (EditText) findViewById(R.id.edit);
        tx= (TextView) findViewById(R.id.tx);
    }
    @Override
    protected void onDestroy() {
        super.onDestroy();
     String input=edit.getText().toString();
        save(input);
    }
//保存数据
思想：通过openFileOutput方法，得到一个FileOutputStream对象，将其包裹在
OutputStreamWriter上，也生成一个对象，继续包裹在BufferedWriter上，得到一个对象
调用write()方法，把数据传入

    private void save(String input) {
        FileOutputStream fileout=null;
        BufferedWriter writer=null;
        try {
   //data:文件名 Context.MODE_PRIVATE:访问权限
            fileout=openFileOutput("data", Context.MODE_PRIVATE);
            writer=new BufferedWriter(new OutputStreamWriter(fileout));
            writer.write(input);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        finally {
            if(writer!=null)
                try {
                    writer.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
        }
    }
    public void doclick(View v) {
        switch (v.getId()) {
            case R.id.bt:
            String text = load();
            tx.setText(text);
        }
    }
//取出数据
    public String load()
    {
        FileInputStream input=null;
        BufferedReader read=null;
//StringBuilder的对象的append方法可以将字符连接起来
        StringBuilder content=new StringBuilder();
        try {
            input=openFileInput("data");
            read=new BufferedReader(new InputStreamReader(input));
            String line="";
            while((line=read.readLine())!=null){
                content.append(line);
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return content.toString();
    }
}

File文件存储