请帮忙书写完整代码要求：一个Activity上有一个输入框和一个保存按钮。输入框用于输入内容点击保存按钮将输入框内的数据保存到以datatxt命名的文件中弹Toast提示数据存储成功。同时界面上还需要有一个文本框和一个读取数据按钮。点击读数按钮将上一步存入datatxt中的数据取出并在文本框中显示文件中的内容。

以下是完整的代码：

MainActivity.java

import androidx.appcompat.app.AppCompatActivity;

import android.content.Context;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStreamReader;

public class MainActivity extends AppCompatActivity {

    EditText editText;
    Button saveButton, readButton;
    TextView textView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        editText = findViewById(R.id.editText);
        saveButton = findViewById(R.id.saveButton);
        readButton = findViewById(R.id.readButton);
        textView = findViewById(R.id.textView);

        saveButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String data = editText.getText().toString();
                saveData(data);
                Toast.makeText(MainActivity.this, "数据存储成功", Toast.LENGTH_SHORT).show();
            }
        });

        readButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String data = readData();
                textView.setText(data);
            }
        });
    }

    private void saveData(String data) {
        try {
            FileOutputStream fos = openFileOutput("data.txt", Context.MODE_PRIVATE);
            fos.write(data.getBytes());
            fos.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private String readData() {
        String data = "";
        try {
            FileInputStream fis = openFileInput("data.txt");
            InputStreamReader isr = new InputStreamReader(fis);
            BufferedReader br = new BufferedReader(isr);
            String line;
            while ((line = br.readLine()) != null) {
                data += line;
            }
            br.close();
            isr.close();
            fis.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return data;
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="16dp"
    tools:context=".MainActivity">

    <EditText
        android:id="@+id/editText"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="输入内容"
        android:inputType="text" />

    <Button
        android:id="@+id/saveButton"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="保存" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="16dp"
        android:padding="16dp"
        android:text="" />

    <Button
        android:id="@+id/readButton"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="读取数据" />

</LinearLayout>