I read in the doc that the Hibernate libraries actually implement it's own version of Set. I'm wandering if this implementation's contains(Object o) method calles .equals() on the members in the Set (like it is meant to according to the definition of the contains(Object o) function).

thanks

Yes, we also constantly remember people to implement equals()/hashCode() correctly.

What is the correct way to implement the equals()? Are there any common problems people run into when using it? My problem is that calling set's contains() doesn't call equals() in the objects in Set.

thanks
Stephane

Yes, we have an outdated text on the wiki that says "implement equals using the persistent identifier". This is not a good design, use the "semi"-unique attributes of your persistent class to implement it. For example, if I have an "Item" class and it has a "name" String and "created" Date, I can use both to implement a good equals() method.

The combination of both fields is stable enough for the duration an Item may be in a Set. It is not as good as a primary key, but it's certainly a weaker candidate key. Don't use the persistent identifier (the primary key) for equals(), as it will not have a value assigned if an object is new.

Calling contains() calls equals() on the objects in the Set. If it doesn't, your Java is broken. ;)