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");  
}

This is how you save your data when the system deletes it on rotation.

By default, when the screen is rotated your Activity is killed and restarted. To make sure no data is lost, you need to properly save and restore your data using the lifecycle methods. See Saving Persistent State.