how to change the string values of sting.xml file

i hava a layout file like test.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent" android:layout_height="match_parent">
<TextView android:layout_width="wrap_content"
        android:layout_height="wrap_content" android:id="@+id/test_string" />
</RelativeLayout>

and java file like this. test1.java

public class test1 extends Activity {
String t开发者_Go百科emp="This is String"; //which change dynamically
TextView tempview;
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    tempview=(TextView)findViewById(R.id.test_string);
    tempview.setText(temp);
    setContentView(R.layout.test);
    }
}

what i am trying to do is show the value of temp in activity as above code. but it throws an NullPointerException. so how to do. how to set the values of sting.xml??? thanks in advance..

setContentView(R.layout.test); should come before (TextView)findViewById(R.id.test_string);