Rule Definition
Hibernate supports array usage: the details of an array mapping are virtually identical to those of a list. However, we very strongly recommend against the use of arrays, since arrays cannot be lazily initialized: there is no way to proxy an array at the virtual machine level. Lists, maps, and sets are the most efficient collection types. Even in cases where we need to retain order, we use java.util.List because the size of the array can not grow dynamically but it can grow dynamically in the case of List. Arrays cannot be lazily initialized. The idea of disabling proxies or lazy loading is considered a bad practice in Hibernate. It can result in a lot of data being fetched from a database and stored in memory, irrespective of the need for it.

Remediation
Use lists, maps, bags, idbags and sets depending on your case.

Violation Code Sample

---> sample.hbm.xml
<hibernate-mapping >
  
  <class name="A" table ="A">
    <id name="id" column="A_ID">
      <generator class="increment"/>
    </id>
     <array name="Bitems" cascade="all" fetch="join"> // VIOLATION
      <key column="A_ID"/>
      <one-to-many class="B"/>
    </array>
  </class>

  <class name="B" table="B" lazy="true">
    <id name="id" column="B_ID">
      <generator class="increment"/>
    </id>
  </class>

</hibernate-mapping


---> sample.java
@Entity
public class A{
    // ...

    @OneToMany()
    private Array<B> Bitems;
}

@Entity
public class B{
    // ...

}

Fixed Code Sample

<hibernate-mapping >
  
  <class name="A" table ="A"> 
    <id name="id">
      <generator class="increment"/>
    </id>

    // FIXED with a list (it could have been set, map, idbag or bag)
    <list name="Bitems" cascade="all" fetch="join"> 
      <key column="B_ID"/>
      <list-index column="ID"/>
      <one-to-many class="B"/>
    </list>
  </class>

  <class name="B" table="B" lazy="true">
    <id name="id" column="B_ID">
      <generator class="increment"/>
    </id>
  </class>

</hibernate-mapping>


---> sample.java
@Entity
public class A{
    // ...

    @OneToMany()
    private List<B> Bitems;
}

@Entity
public class B{
    // ...

}

Hibernate in Action (ISBN 1932394-15-X) p 214 http://srcrr.com/java/hibernate/3.6.2/reference/org/hibernate/collection/PersistentArrayHolder.html