Primary Key class?

[Amit Batra]

I was reading on p333 and it mentions a "primary key class must be serializable and public". Where is this primary key class defined/shown in the book? and why must it be public and serializable?

[Valentin Crettaz]

Where is this primary key class defined/shown in the book?

Which book ?

and why must it be public and serializable?

Actually, the EJB 2.1 spec says that the primary key class should be public (10.6.13 and 10.8.2) but it doesn't mention that it should be serializable, only that the class should be a legal value type in RMI-IIOP (9.8), which implies that it should be Serializable.

[Amit Batra]

Valentin thansk for answering my second second quesry. The book Im talking about is The HFEJB. I was thinking that an example of the primary key class would be shown somewhere but I guess its not.

[Valentin Crettaz]

There is one example of a compound primary key class in chapter 10 of RMH's Enterprise Java Beans book.

Here it is:

public class ShipPK implements java.io.Serializable {
    public String name;
    public String registration;
    
    public ShipPK(){
    }   
    public ShipPK(String name, String registration) {
        this.name = name;
        this.registration = registration;
    }
    public String getName() {
        return name;
    }
    public String getRegistration() {
        return registration;
    }
    public boolean equals(Object obj) {
        if (obj == null || !(obj instanceof ShipPK))
            return false;
        
        ShipPK other = (ShipPK)obj;
        if(this.name.equals(other.name) and 
            this.registration.equals(other.registration))
            return true;
        else
            return false;
        
    }
    public int hashCode() {
        return name.hashCode()^registration.hashCode();
    }
 
    public String toString() {
        return name+" "+registration;
    }
 
}

[Amit Batra]

Hi Valentin,
Thanks for your response, but Im afraid I must trouble you once again. Could you please explain me why we have the equals and hashcode method defined in the primary key class?. im sort of lost of the whole what the role of the primary key class is in the scheme of things.

[Rajan Murugan]

you would go in for primary key class if your primary key (the key with which you identify your entity uniquely) is made up from more than one field of the table or tables (in case the primary key fields are from different tables).

hashCode is more importantly used in storing into collections and other similar purposes where hashcode may be of use.

equals is to check if two keys are same so that we may know if two entities are equal.

go through the code given it will make things more clear and some of the stuff will be self explanatory

[Valentin Crettaz]

Originally posted by Amitabha Batranab:
Hi Valentin,
Thanks for your response, but Im afraid I must trouble you once again. Could you please explain me why we have the equals and hashcode method defined in the primary key class?. im sort of lost of the whole what the role of the primary key class is in the scheme of things.

No problem. If you read the sections I mentioned, you'll see that it is mandatory for the primary key class to override equals() and hashcode().

[Rajan Murugan]

hi valentin,

Can you point out situations where the container/stub/client may be making use of hashCode() and equals().this is wrt Entity beans especially.