Creating Mappings with Hibernate XML Files - Beginning Hibernate: From Novice to Professional - page 140

Components
Lying somewhere between entities and values are component types. When the class represen-
tation is simple and its instances have a strong one-to-one relationship with instances of
another class, then it is a good candidate to become a component of that other class.
The component will normally be mapped as columns in the same table that represents
most of the other attributes of the owning class, so the strength of the relationship must justify
this inclusion. In the following code, the MacAddress class might a good candidate for a com-
ponent relationship.

public class NetworkInterface {
public int id;
public String name;
public String manufacturer;
public MacAddress physicalAddress;

}

The advantage of this approach is that it allows you to dispense with the primary key of
the component and the join to its containing table. If a poor choice of component is made
(for example, when a many-to-one relationship actually holds), then data will be duplicated
unnecessarily in the component columns.

Values
Everything that is not an entity or a component is a value. Generally, these correspond to the
data types supported by your database, the collection types, and, optionally, some user-
defined types.
The details of these mappings will be vendor-specific, so Hibernate provides its own value
type names; the Java types are defined in terms of these (see Table 7-1).

Table 7-1. The Standard Hibernate 3 Value Names

Hibernate 3 Type Corresponding Java Type

Primitives and Wrappers
integer

int, java.lang.Integer

long long, java.lang.Long

short short, java.lang.Short

float float, java.lang.Float

double double, java.lang.Double

character char, java.lang.Character

byte byte, java.lang.Byte

boolean, yes_no, true_false boolean, java.lang.Boolean

Other Classes
string java.lang.String

date, time, timestamp java.util.Date

calendar, calendar_date java.util.Calendar