Notes on 'Refactoring' -- 5.1 Seperate Query from Modifier
Before Refactoring

  getPersonAndIncreaseCounter(){     counter ++;     return person;   }

After Refactoring

  getPerson(){     return person;   }    increaseCounter{     counter ++;  }

Benefits
You can call getPerson() as often as you like. You have a lot less to worry about.

Exception
It's OK to change personCache in getPerson() method.