Problem with the List - Java

Question

I am trying to create a new instance of Couple with the given name and gender and add to the collections of couples, in the addCouple method. I have another class called Couple. In that class I have getters and Setters one for name and the gender. I tried to use the bulk operation for the list:

List<Dating> list1 = new ArrayList<Dating>(this.addCouple);

but I got an error "nonstatic variable this cannot be referenced from a static context". I then tried to use Collection.sort then printout the list. I got the same error message. So I believe I do not know how to use this.addList. Could someone tell me how to use it. Should I be using this.addList? Thanks in advance.

public class Dating
{

  private List<Male> maleList;
  private List<Female> femaleList; 


  public Dating()
  {

    super();
    maleList = new ArrayList<Single>();
    femaleList = new ArrayList<Single>();
  }


  public void lists()
  { 
   this.addList("Jack","Male",'m');
   this.addList("Mike","Male",'m'); 

   this.addList("Lynda","Female",'f'); 
   this.addList("Katie","Female",'f'); 
  }


   public static void addCouple (String aName, char aGender)
   {
      Collections.sort(this.addList);
      for (Couple group : this.addList)
      {
         System.out.println(" " + group.getName() + " " + group.getGender());
      }

   }

Answer 1

You have to make your members static or you must remove the static flag from your function. You can not mix static with non static stuff, roughly said.

Answer 2

Your addCouple is declared as a static method. There is no this for static methods, because they don't belong to an instance. They belong to a class.

Answer 3

I think you have much bigger problems than that. Classes Male, Female, Single? Those are attributes of a Person class, not classes in and of themselves. Your design needs rework.

You need Person and Couple classes. You also need a model that reflects the real world. Like it or not, you can have Male-Male and Female-Female couples.

I'd write it like this. As you can see, List works perfectly:

Gender.java:

public enum Gender
{
    MALE, FEMALE;
}

MaritalStatus.java:

public enum MaritalStatus
{
    SINGLE, MARRIED, DIVORCED, WIDOWED, SEPARATED;
}

Person.java:

import java.text.DateFormat;
import java.util.Date;

public class Person
{
    private String name;
    private Date birthdate;
    private Gender gender;
    private MaritalStatus maritalStatus;

    public Person(String name)
    {
        this(name, new Date(), Gender.MALE, MaritalStatus.SINGLE);
    }

    public Person(String name, Gender gender)
    {
        this(name, new Date(), gender, MaritalStatus.SINGLE);
    }

    public Person(String name, Date birthdate)
    {
        this(name, birthdate, Gender.MALE, MaritalStatus.SINGLE);
    }

    public Person(String name, Date birthdate, Gender gender)
    {
        this(name, birthdate, gender, MaritalStatus.SINGLE);
    }

    public Person(String name, Date birthdate, Gender gender, MaritalStatus maritalStatus)
    {
        if ((name == null) || (name.trim().length() == 0))
            throw new IllegalArgumentException("name cannot be blank or null");

        this.name = name;
        this.birthdate = ((birthdate == null) ? new Date() : new Date(birthdate.getTime()));
        this.gender = gender;
        this.maritalStatus = maritalStatus;
    }

    public String getName()
    {
        return name;
    }

    public Date getBirthdate()
    {
        return new Date(birthdate.getTime());
    }

    public Gender getGender()
    {
        return gender;
    }

    public MaritalStatus getMaritalStatus()
    {
        return maritalStatus;
    }

    @Override
    public boolean equals(Object o)
    {
        if (this == o)
        {
            return true;
        }
        if (o == null || getClass() != o.getClass())
        {
            return false;
        }

        Person person = (Person) o;

        if (!birthdate.equals(person.birthdate))
        {
            return false;
        }
        if (gender != person.gender)
        {
            return false;
        }
        if (maritalStatus != person.maritalStatus)
        {
            return false;
        }
        if (!name.equals(person.name))
        {
            return false;
        }

        return true;
    }

    @Override
    public int hashCode()
    {
        int result = name.hashCode();
        result = 31 * result + birthdate.hashCode();
        result = 31 * result + gender.hashCode();
        result = 31 * result + maritalStatus.hashCode();
        return result;
    }

    @Override
    public String toString()
    {
        return "Person{" +
               "name='" + name + '\'' +
               ", birthdate=" + DateFormat.getDateInstance(DateFormat.MEDIUM).format(birthdate) +
               ", gender=" + gender +
               ", maritalStatus=" + maritalStatus +
               '}';
    }
}

Couple.java:

public class Couple
{
    private Person ying;
    private Person yang;

    public Couple(Person ying, Person yang)
    {
        this.ying = ying;
        this.yang = yang;
    }

    public Person getYing()
    {
        return ying;
    }

    public Person getYang()
    {
        return yang;
    }

    @Override
    public String toString()
    {
        return "Couple{" +
               "ying=" + ying +
               ", yang=" + yang +
               '}';
    }
}

Dating.java:

import java.util.ArrayList;
import java.util.List;


public class Dating
{
    private List<Person> individuals = new ArrayList<Person>();
    private List<Couple> couples     = new ArrayList<Couple>();

    public static void main(String[] args)
    {
        Dating dating = new Dating();

        dating.addIndividual(new Person("Jack"));
        dating.addIndividual(new Person("Mike"));
        dating.addIndividual(new Person("Lydia", Gender.FEMALE));
        dating.addIndividual(new Person("Kate", Gender.FEMALE));

        System.out.println(dating);
    }

    public void addIndividual(Person p)
    {
        this.individuals.add(p);
    }

    public void removeIndividual(Person p)
    {
        this.individuals.remove(p);
    }

    public Person findIndividual(String name)
    {
        Person found = null;

        if (name != null)
        {
            for (Person p : this.individuals)
            {
                if (name.equals(p.getName()))
                {
                    found = p;
                    break;
                }
            }
        }

        return found;
    }

    @Override
    public String toString()
    {
        return "Dating{" +
               "individuals=" + individuals +
               ", couples=" + couples +
               '}';
    }
}

Answer 4

You'd better be off with creating a "Person" class which might roughly look like this:

public class Person
{
    private String name;
    private boolean male; // or use an enum GENDER if you plan to do more than male/female

    public Person(String name, boolean male)
    {
        this.name = name;
        this.male = male;
    }

    // [...] getters and setters

    public String toString()
    {
            return name + " " + (male ? "male" : "female");
    }
}

and, depending on what you actually want to do... (a little bit more information would be good)

public class Dating
{
    private List<Person> persons;
    //[...] constructor

    public void addWhateverYouMeanWithCouple(String name, boolean male)
    {
        this.persons.add(new Person(name, male));
        System.out.println(persons);
    }
}

I really don't know what you are looking for, this is the only bit of code I can provide you, though I still think it's not exactly what you are looking for.

If you want to sort the List of Persons you will have implement Comparable<Person> (see Comparable JavaDoc) in the Person class and provide some logic to compare two Persons (e.g. using name.compareTo(otherName)).

If you actually want to have "Couples" or Pairs, have a look at HashMap.

Answer 5

attually just two lines of code was required. I was difficult to explain in first instance. Thanks for all the relies.