代码如下所示：

public class MainActivity extends AppCompatActivity {
private EditText editText;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        editText= (EditText) findViewById(R.id.edit);
        String input=load();
        if(!TextUtils.isEmpty(input)){
            editText.setText(input);
            editText.setSelection(input.length());
        }
    }

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

    public void save(String inputstring)
    {
        FileOutputStream out=null;
        BufferedWriter writer=null;
        try {
            out=openFileOutput("shuju", Context.MODE_PRIVATE);//Context.MODE_PRIVATE是如果有同名的文件，则覆盖原文件的内容，Context.MODE_APPEND则表示如果该文件存在，就往文件里面追加内容，不存在就创建文件
            writer=new BufferedWriter(new OutputStreamWriter(out));
            writer.write(inputstring);
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            if(writer!=null)
            {
                try {
                    writer.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
    public String load()
    {
        FileInputStream in=null;
        BufferedReader reader=null;
        StringBuffer content=new StringBuffer();
        try {
            in=openFileInput("shuju");
            reader=new BufferedReader(new InputStreamReader(in));
            String line="";
            while ((line=reader.readLine())!=null){
                content.append(line);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            if(reader!=null){
                try {
                    reader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return content.toString();
    }
}