The <generator> sub-element of <id> specifies how to generate the unique identifier for the persistent objects. Hibernate defines many generator classes which implement org.hibernate. id.IdentifierGenerator interface. It is also possible to write a generator class implementing this interface. The type of generator is indicated in the <generator> element using class attribute as follows:
<generator class=”generator type”></generator>
Some of the built-in generator classes with their functions are discussed in Table 23.2:
Source: Uttam Kumar Roy (2015), Advanced Java programming, Oxford University Press.