/** A database of people. */
public class PersonDB{ 
  private Person[] people;
  
  /** Creates a default database with 3 people. */
  public PersonDB(){
    people = new Person[] {new Person("jo",25), 
                           new Person("flo",18),
                           new Person("mo", 19)};
  }
  
  public PersonDB(Person [] p){
    people = p;
  }
  
  /** Calculates and returns the average age. */
  public double getAverageAge(){
    double sum = 0.0;
    int numOfEntries = 0;
    if(people.length == 0 || people == null){
      return sum;
    }
    
    for(int i = 0; i < people.length; i++){
        if(people[i] != null){
            sum = sum + people[i].getAge();
            numOfEntries++;
        }
        else{
            System.out.println("Null entry");
        }
    }
    return sum/numOfEntries; //change approriately
  } 
}