/**
* @hibernate.class table="Cat"
* @hibernate.cache usage="nonstrict-read-write"
*/
class Cat
{
    // Synthentic Identity (unique enforced by database)
    Integer id;
    /**
     * @hibernate.id generator-class="native" column="euid"
     */
    public Integer getId()
    {
        return id;
    }
    public void setId(Integer id)
    {
   this.id = id;
    }

    // store this otherwise evil things happen with sets
    private int hashcode = super.hashCode();
    /**
     * @hibernate.property not-null="true"
     */
    public int getHashCode()
    {
        return hashcode;
    }
    public void setHashCode(int hashcode)
    {
        this.hashcode = hashcode;
    }
    public int hashCode()
    {
        return hashcode;
    }
    public boolean equals(Object obj)
    {
        // (1) same instance (creation or same session)
        if (obj == this) return true;

        // (2) hashcode must match (we honour hashcode from creation)
        if (hashcode != obj.hashCode()) return false;

        // (3) hashcode might match, but duplicate hashcode the same
        if (obj instanceof Cat)
        {
            Cat le = (Cat)obj;

            // (4) if we dont have an id, then we're not persisted and rule (1) is authorative
            if (this.id == null || le.getId() == null) return false;

            // (5) we've been persisted, check our identifier
            if (this.id.intValue() == le.getId().intValue()) return true;
        }

        // (6) no
        return false;
    }
}

class Cat
{
    ... as above ...

    CatID catid = new CatID();

    class CatID extends BaseID
    {
        CatID() { super(0); }
        public int hashCode() { return hashcode; }
        public boolean legal() { return id != null; }
        public int intValue() { return id.intValue(); }
    }
    public BaseID getCatID() { return catid; }
}

public class BaseID
{
    int value, hashcode;
    public BaseID(int value, int hashcode) { this.value = value; this.hashcode = hashcode;}
    public int intValue() { return value; }
    public boolean legal() { return true; }
    public int hashCode() { return hashcode; }
    public boolean equals(Object o)
    {
        if (o == this) return true;
        if (!legal()) return false;
        if (o instanceof BaseID)
        {
            BaseID bid = (BaseID) o;
            if (!bid.legal()) return false;
            return intValue() == bid.intValue();
        }
        return false;
    }
}