@Entity
@Table(name="TBL_PRODUCTS")
public class TblProducts implements Serializable
{
   @Id
   @Column(name="PRODUCT_ID")   
   private BigDecimal productId;

   @Column(name="PRODUCT_NAME")   
   private String productName;

   @JoinColumn(name="BRAND_NAME")   
   private String brandname;
   
   @OneToOne(fetch=FetchType.LAZY,mappedBy="tblProducts")   
   private TblCellphone tblCellphone;

   @OneToOne(fetch=FetchType.LAZY,mappedBy="tblProducts")
   private TblTelevision tblTelevision;

}

@Entity
@Table(name="TBL_CELLPHONE")
public class TblCellphone implements Serializable
{
   @Id
   @Column(name="PRODUCT_ID")   
   private BigDecimal productId;

private String camera;

. . .

@OneToOne(optional=false)
     @JoinColumn(name="PRODUCT_ID")   
private TblProducts tblProducts;
}

@Entity
@Table(name="TBL_TELEVISION")
public class TblTelevision implements Serializable
{
   @Id
   @Column(name="PRODUCT_ID")
   private BigDecimal productId;

   @Column(name="SCREEN_SIZE")
   private String screenSize;
   
   . . .

   @OneToOne(optional=false)
   @JoinColumn(name="PRODUCT_ID")   
   private TblProducts tblProducts;
}

java.lang.NullPointerException
   at org.hibernate.cfg.OneToOneSecondPass.doSecondPass(OneToOneSecondPass.java:135)
   at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1130)
   at org.hibernate.cfg.AnnotationConfiguration.secondPassCompile(AnnotationConfiguration.java:296)
   at org.hibernate.cfg.Configuration.buildMappings(Configuration.java:1115)
   at org.hibernate.ejb.Ejb3Configuration.buildMappings(Ejb3Configuration.java:1233)
   at org.hibernate.ejb.EventListenerConfigurator.configure(EventListenerConfigurator.java:154)
   at org.hibernate.ejb.Ejb3Configuration.configure(Ejb3Configuration.java:869)
   at org.hibernate.ejb.Ejb3Configuration.configure(Ejb3Configuration.java:407)
   at org.hibernate.ejb.HibernatePersistence.createContainerEntityManagerFactory(HibernatePersistence.java:126)
   at org.jboss.ejb3.entity.PersistenceUnitDeployment.start(PersistenceUnitDeployment.java:246)
   at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
   at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
   at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
   at java.lang.reflect.Method.invoke(Unknown Source)