@Entity
@Table(name = "parent")
public class Parent implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer parentID;


    @OneToOne(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    @JoinColumn(name="parentID")  //, unique=true, nullable=false, updatable=false
    private Child child;

...
// other column   
...
// setters and getters
...
}

@Entity
@Table(name = "child")
public class Child implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer childID;


    @OneToOne(mappedBy = "child")
    private Parent parent;

...
// other column   
...
// setters and getters
...
}

CREATE TABLE `parent` (
  `parentID` int(11) NOT NULL ,
  `text` varchar(65524) NOT NULL,
  PRIMARY KEY (`parentID`)
);


CREATE TABLE `child` (
  `childID` int(11) NOT NULL,
  `parentID` int(11) NOT NULL ,
  `text` varchar(65524) NOT NULL,
  PRIMARY KEY (`childID`),
  UNIQUE KEY `parentID` (`parentID`),
  KEY `fk_parentID` (`parentID`),
  CONSTRAINT `fk_parentID` FOREIGN KEY (`parentID`) REFERENCES `parent` (`parentID`)
);