Question

I have two classes. One(Person) for getters and setters, and another(People) for compute the data. What is my situation is, I get the data from the DB using ResultSet, then created a person Object to store the row data. Then i created people Object to store all persons.

Each Object created as SET.

while(rs.next())
{
    Set<People> people = new HashSet<people>();
    Person person = new Person();
    String name = rs.getString(2);
    person.setName(name);
    int id = rs.getInt(1);
    person.setId(id);
    String dept = rs.getString(4);
    person.setDept(dept);
    int age = rs.getInt(3);
    person.setAge(age);
    people.add(person);
}
return people;

Now the problem is the last line in the While Loop people.add(person);

It says

The method add(People) in the type Set is not applicable for the arguments (Person)

How can i overcome this problem?

Thanks.

Answer 1

My understandig from your design is that you have a People has-many Person relation, so the People class holds a collection of Person objects. Then I’d expect something like this:

public class Person {
  private String name;
  private Date dateOfBirth;
  // .. more attributes

  // getters and setters

  // overrides of equals, hashcode and toString
}

public class People implements Set<Person> {
  private Set<Person> persons = new HashSet<Person>();

  public boolean add(Person person) {
    return persons.add(person);
  }

  // more methods for remove, contains, ...
}

So in your database related code you wouldn’t need to create another set, because People already has the one you need:

People people = new People();  // or get it, if it's already created
while(rs.next())
{
    Person person = new Person();
    String name = rs.getString(2);
    person.setName(name);
    int id = rs.getInt(1);
    person.setId(id);
    String dept = rs.getString(4);
    person.setDept(dept);
    int age = rs.getInt(3);
    person.setAge(age);
    people.add(person);
}
return people;