By default, when the screen is rotated your Activity is killed and restarted.  See the sample code below to save the state

 

Source:  http://stackoverflow.com/questions/5123407/losing-data-when-rotate-screen

 

//Use onSaveInstanceState(Bundle) and onRestoreInstanceState

@Override
public void onSaveInstanceState(Bundle savedInstanceState) {

  // Save UI state changes to the savedInstanceState.  
  // This bundle will be passed to onCreate if the process is 
  // killed and restarted.

  savedInstanceState.putBoolean("MyBoolean", true); 
  savedInstanceState.putDouble("myDouble", 1.9); 
  savedInstanceState.putInt("MyInt", 1); 
  savedInstanceState.putString("MyString", "Welcome back to Android");   
  // etc. 
  super.onSaveInstanceState(savedInstanceState); 
} 
//onRestoreInstanceState 
    @Override 
public void onRestoreInstanceState(Bundle savedInstanceState) { 
  super.onRestoreInstanceState(savedInstanceState); 
  // Restore UI state from the savedInstanceState. 
  // This bundle has also been passed to onCreate. 
  boolean myBoolean = savedInstanceState.getBoolean("MyBoolean"); 
  double myDouble = savedInstanceState.getDouble("myDouble"); 
  int myInt = savedInstanceState.getInt("MyInt"); 
  String myString = savedInstanceState.getString("MyString"); 
}