public class PracticalTest01MainActivity extends Activity {

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    
    // ...

    if (savedInstanceState != null) {
      String leftCount = savedInstanceState.getString("leftCount");
      if (leftCount != null) {
        leftEditText.setText(leftCount);
      } else {
        leftEditText.setText(String.valueOf(0));
      }
      String rightCount = savedInstanceState.getString("rightCount");
      if (rightCount != null) {
        rightEditText.setText(rightCount);
      } else {
        rightEditText.setText(String.valueOf(0));
      }
    } else {
      leftEditText.setText(String.valueOf(0));
      rightEditText.setText(String.valueOf(0));
    }
  }

  @Override
  protected void onSaveInstanceState(Bundle savedInstanceState) {
    EditText leftEditText = (EditText)findViewById(R.id.left_edit_text);
    EditText rightEditText = (EditText)findViewById(R.id.right_edit_text);
    savedInstanceState.putString("leftCount", leftEditText.getText().toString());
    savedInstanceState.putString("rightCount", rightEditText.getText().toString());
  }
  
  // ...
}