How to write hasCode() & equals(0) methods in Compound Key Class

Question

Hi Java Helpdesk,
I am wondering how to write the hashCode() and equals() methods that is mandatory when creating composite
@IdClass. Below is the combination of primary @Id keys that I would like to make up in a compound key class:
public final class PatientKey implements java.io.Serializable
    private String firstnameId;
    private String SurnameId;
    private String DateOfBirthID;
    private String Sex;
    public int hashCode()
    public boolean equals(Object otherOb)
}The Order application in Java EE 5 Tutorial (page 841) is made up of only 2 primary keys.
Thanks,
Jack

Answer 1

Hi,
Thanks for your very brief response and I had a look at both EqualsBuilder and HashCodeBuilder from the URL links you have provided. These methods may improve the comparison accuracy but I was more interested on how to implement the equals() and hashCode methods when comparing 3 or more primary keys in order to make up a primary key class. Below is my first attempt to compose the PatientPK primary key class:
1. public class PatientPK implements java.io.Serializable {
2.
3.     private String firstName;
4.     private String lastName;
5.     private String dateOfBirth;
6.     private Char sex;
7.
8.     public PatientPK() {}
9.
10.   public PatientPK(String firstName, String lastName, Date dateOfBirth, Char sex)
11.   {
12.       this.firstName = firstName;
13.       this.lastName = lastName;
14.       this.dateOfBirth = dateOfBirth;
15.       this.sex = sex;
16.   }
17.
18.   public String getFirstName() { return this.firstName; }
19.   public void setFirstName(String firstname) { this.firstName = firstName; }
20.
21.   public String getlastName() { return this.lastName; }
22.   public void setLastname(String lastName) { this.lastName = lastName; }
23.
24.   public String getDateOfBirth() { return this.dateOfBirth; }
25.   public void setDateOfBirth(String dateOfBirth) { this.dateOfBirth = dateOfBirth; }
26.
27.   public Char getSex() { return this.sex; }
28.   public void setSex(String sex) { this.sex = sex; }
29.
30.   public boolean equals(Object obj)
31.   {
32.       if (obj == this) return true;
33.       if (!(obj instanceof PatientPK)) return false;
34.       PatientPK pk = (PatientPK) obj;
35.       if (!firstName.equals(pk.firstName)) return false;
36.       if (!lastName.equals(pk.lastName)) return false;
37.       if (!dateOfBirth.equals(pk.dateOfBirth)) return false;
38.       if (!sex.equals(pk.sex)) return false;
39.       return true;
40.   }
41.
42.   public hashCode()
43.   {
44.       return firstName.hashCode() + lastName.hashCode() + dateOfBirth.hashCode() + sex.hashCode();
45.   }
46.}Please advice whether both these equals() and hashCode() implementations are correct.
Thanks in advance,
Jack