文本文件数据输入与读取

步骤1
两个Edittext用来作为输入和获取的媒介<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.xun.savedata.MainActivity">

<EditText
android:id="@+id/editText"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="16dp"
android:layout_marginTop="24dp"
android:ems="10"
android:inputType="textPersonName"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintTop_toTopOf="parent" />

<EditText
android:id="@+id/editText2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="88dp"
android:ems="10"
android:inputType="textPersonName"
app:layout_constraintHorizontal_bias="0.55"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toBottomOf="@+id/editText" />

<Button
android:id="@+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:text="Button"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.498" />
</android.support.constraint.ConstraintLayout>步骤2

openFileOutput()

方法返回的是一个

FileOutputStream

对象，参数1：文件名 参数2：MODE_PRIVATE和MODE_APPEND。其中MODE_PRIVATE是默认的操作模式，表示当指定同样文件名的时候，所写入的内容将会覆盖原文件中的内容，而MODE_APPEND则表示如果该文件已存在，就往文件里面追加内容，不存在就创建新文件。
new BufferedReader/new BufferedWriter是获取字符串数据，并以相应方式输出
public class MainActivity extends AppCompatActivity {
private EditText editText;
private EditText editText1;
private String a;
private String inputText;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
editText=(EditText)findViewById(R.id.editText);
editText1=(EditText)findViewById(R.id.editText2);
inputText = intput();
editText1.setText(inputText);
}

@Override
protected void onDestroy() {
super.onDestroy();
a=editText.getText().toString();
save(a);
}
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 intput(){
FileInputStream intpu
4000
t=null;
BufferedReader reader=null;
StringBuilder stringBuilder=new StringBuilder();
try {
intput = openFileInput("data");
reader=new BufferedReader(new InputStreamReader(intput));
String line="";
while ((line = reader.readLine()) != null) {
stringBuilder.append(line);
}

} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (reader != null) {
reader.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
return stringBuilder.toString();
}

}