Save important app content into xml resource

I'm completely new to what I'm doing and I actualy think I'm doing it totaly wrong.

Anyway... I was trying to make a test app where you write some String into editText and the application should save it into the next launch.

I tryed to do that through xml resource and it seems completely messed up. Please, help me!

This is how my layout looks like:

<RelativeLayout xmlns:android="http://ift.tt/nIICcg"
xmlns:tools="http://ift.tt/LrGmb4"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".Filedemo" >

<Button
    android:id="@+id/button1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_centerHorizontal="true"
    android:layout_marginBottom="130dp"
    android:text="finish" />

<EditText
    android:id="@+id/editText1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="111dp"
    android:ems="10"
    android:inputType="textMultiLine" >

    <requestFocus />
</EditText>

</RelativeLayout>

This is the xml I'm trying to save the string into:

<?xml version="1.0" encoding="utf-8"?>
<resources>
<item name="thetext" type="id"/>
<item name="textik" type="whatever">
    <thetext>hello</thetext>
</item>
</resources>

...and finaly my java code:

public class Filedemo extends Activity {
private Document doc;
private EditText etext;
private Button but;

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

    etext = (EditText)findViewById(R.id.editText1);
    but = (Button)findViewById(R.id.button1);

    Context context = getApplicationContext();   
    InputStream istream = context.getResources().openRawResource(R.id.thetext);  

    DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance();    
    DocumentBuilder docBuilder = null;                                           
    try {                                                                      
        docBuilder = docFactory.newDocumentBuilder();                          
    } catch (ParserConfigurationException e1) {                            
        // TODO Auto-generated catch block                              
        e1.printStackTrace();                                        
    }                                                             
    try {                                                    
        doc = docBuilder.parse(istream);                             
    } catch (SAXException e) {                                       
        // TODO Auto-generated catch block                           
        e.printStackTrace();                                    
    } catch (IOException e) {                             
        // TODO Auto-generated catch block                 
        e.printStackTrace();                                    
    }                                                                 
    final Node textik = doc.getElementsByTagName("thetext").item(1);          

    etext.setText(textik.getTextContent());

    but.setOnClickListener(new OnClickListener(){
        public void onClick(View v){
            String s = etext.getText().toString();
            textik.setTextContent(s);
            System.exit(0);
        }
    });
}

}