First steps and detailed concepts Java Persistence api

import
javax.persistence.Entity;
import
javax.persistence.GeneratedValue;
import
javax.persistence.GenerationType;
import
javax.persistence.Id;
@Entity
public
class
Person {
@Id
@GeneratedValue
(strategy = GenerationType.IDENTITY)
private
int
id;
private
String name;
public
String getName() {
return
name;
}
public
void
setName(String name) {
this
.name = name;
}
}
The database controls the ID generation, JPA does not act on the id at all. Thus in order to retrieve the id from the 
databse an entity needs to be persisted first, and after the transaction commits, a query is executed so as to 
retrieve the generated id for the specific entity. This procedure leads to a small performance degradation, but not 
something troublesome.
The aforementioned id generation approach does not allow allocating ids in memory. We will examine what this ids 
allocation means in the following chapters.
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Sequence
The Sequence approach can be configured like below:
import
javax.persistence.Entity;
import
javax.persistence.GeneratedValue;
import
javax.persistence.GenerationType;
import
javax.persistence.Id;
import
javax.persistence.SequenceGenerator;
@Entity
@SequenceGenerator
(name = Car.CAR_SEQUENCE_NAME, sequenceName = Car.CAR_SEQUENCE_NAME, initialValue = 
10
, 
allocationSize = 
53
)
public
class
Car {
public
static
final
String CAR_SEQUENCE_NAME = 
"CAR_SEQUENCE_ID"
;
@Id
@GeneratedValue
(strategy = GenerationType.SEQUENCE, generator = CAR_SEQUENCE_NAME)