@Column annotation and constraints in db

@Column(unique = true, nullable = false)
private Date startDate;

This annotation is description on startDate column when reading java file.
It is not used to stop inserting or updating database with false values, if you do not have constraints on table!
It can be used for generating table from entity class.

1 exception to the above rule:
If you try insert null into not null field declared in annotation it will throw Exception!