java io

public class MainActivity extends AppCompatActivity {
    private EditText edit;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
      edit = (EditText) findViewById(R.id.edit);
       String inputText = load();
        if (!TextUtils.isEmpty(inputText)) {
           edit.setText(inputText);
           edit.setSelection(inputText.length());
       Toast.makeText(this, "Restoring succeeded", Toast.LENGTH_SHORT).show();
      }
      

    @Override
    protected void onDestroy() {
        super.onDestroy();
        String inputText = edit.getText().toString();
        save(inputText);
    }

    public void save(String inputText) {
        FileOutputStream out = null;
        BufferedWriter writer = null;
        try {
            out = openFileOutput("data", Context.MODE_PRIVATE);
            writer = new BufferedWriter(new OutputStreamWriter(out));
            writer.write(inputText);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (writer != null) {
                    writer.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    public String load() {
        FileInputStream in = null;
        BufferedReader reader = null;
        StringBuilder content = new StringBuilder();
        try {
            in = openFileInput("data");
            reader = new BufferedReader(new InputStreamReader(in));
            String line = "";
            while ((line = reader.readLine()) != null) {
                content.append(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (reader != null) {
                try {
                    reader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return content.toString();
    }

}

sharedpreferences
context class > getSharedPreferences(文件名,MODE_PRIVATE); 沒這文建會自己創一個
Activity class>getPreferences(MODE_PRIVATE); 文件名會拿你activity命名

  Button saveData= (Button) findViewById(R.id.save);
        Button getData=(Button) findViewById(R.id.get);
        saveData.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                SharedPreferences.Editor editor=
                        getSharedPreferences("datat",MODE_PRIVATE).edit();
                //指定名稱 並調用對象添加數據
                editor.putString("name","tom");
                editor.apply();//提交

            }
        });
        getData.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                SharedPreferences preferences=getSharedPreferences("datat",MODE_PRIVATE);
                String name = preferences.getString("name","");
                Log.d("Mainactivity", "onClick: "+name);
            }
        });
    }