need help on question on sessions

[Niranjan Deshpande]

4. Which of the following methods will be invoked on a session attribute that
implements appropriate interfaces when the session is invalidated? (Select one)
a sessionDestroyed of HttpSessionListener
b attributeRemoved of HttpSessionAttributeListener
c valueUnbound of HttpSessionBindingListener
d sessionWillPassivate of HttpSessionActivationListener
Answer: c
Explanation
The HttpSessionListener and HttpSessionAttributeListener are configured
in the deployment descriptor. Therefore, even if a session attribute implements
these interfaces, the sessionDestroyed() and attributeRemoved()
methods will not be called on that attribute.

in my opinion, the anwer is b - since the question asks "...invoked on a session attribute...."

also the explanation doesnt make any sense.

please explain.

[Christophe Verré]

Attributes implement HttpSessionBindingListener, not HttpSessionAttributeListener.
The question is about "methods will be invoked on a session attribute". So it will not be 'b'.

[Rick Roberts]

The following class implements HttpSessionBindingListener which will allow it to be notified when added to a session as an attribute, or removed from a session.

public class Dog implements HttpSessionBindingListener{
  private String breed;
 
  public Dog(String breed){
    this.breed=breed;
  }
 
  public String getBreed(){
    return breed;
  }
 
  public void valueBound(HttpSessionBindingEvent evt){
    //runs when this class is added to a session "as an attribute"
  }
 
  public void valueUnbound(HttpSessionBindingEvent evt){
    //runs when this "attribute" is removed from the session
  }

[ October 18, 2006: Message edited by: Rick Roberts ]