What is the use of generating getters and setters in a class annotated with @Entity (Hibernate)?

What is the use of generating getters and setters in a class annotated with @Entity (Hibernate)?
When do they get invoked?

@Entity
@Table(name="student")
public class Student {

	@Id
	@GeneratedValue(strategy = GenerationType.IDENTITY)
	@Column(name="id")
	private int id;
	private String firstName;
	private String lastName;
	public Student() {
	}

	public Student(String firstName, String lastName) {
		this.firstName = firstName;
		this.lastName = lastName;
	}

	public String getFirstName() {
		return firstName;
	}
	public void setFirstName(String firstName) {
		this.firstName = firstName;
	}
//other getters and setters
}

As soon as your fields are private then you need getters and setters to access them outside of the entity class.

By default Hibernate uses public getters and setters to access entity's attributes, which is considered to be a common approach.

However, it is not strictly required by Hibernate. If your fields are public, then you can tell Hibernate to access those fields directly (through access option). In other hand, having private, default or protected fields/getters/setters, Hibernate is able to deal with them too (through refection, I think).

From Hibernate reference:

> 2.1.3. Declare getters and setters for persistent attributes

> Standard, portable JPA essentially requires this. Otherwise your model would
> violate the requirement quoted above in regards to accessing the
> entity persistent state fields directly from outside the entity
> itself.
>
> Although Hibernate does not require it, it is recommended to follow
> JavaBean conventions by defining getters and setters for you entities
> persistent attributes. You can still tell Hibernate to directly access
> the entity's fields.
>
> Attributes (whether fields or getters/setters) need not be declared
> public. Hibernate can deal with attributes declared with public,
> protected, package or private visibility. Again, if wanting to use
> runtime proxy generation for lazy loading the visibility for the
> getter/setter should be at least package visibility.