public abstract class MyClass<E extends MyAbstractEntity> implements Serializable{
   
   private static final long serialVersionUID = 2832228828007049949L;
   
   private Long id;
   protected E myEntity;
   
         
   @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
   public Long getId() {
      return id;
   }
   @SuppressWarnings("unused")
   private void setId(Long id) {
      this.id = id;
   }
   
      
   @OneToOne(fetch=FetchType.LAZY,cascade=CascadeType.ALL)
   public E getMyEntity() {
      return myEntity;
   }
   @SuppressWarnings("unused")
   private void setMyEntity(M myEntity) {
      this.myEntity = myEntity;
   }
}

public class MyEspecificClass extends MyClass<MyEspecificEntity>{

   private static final long serialVersionUID = 6451465817583035678L;

...Some specific methods...
   
}

public abstract class MyClass<E extends MyAbstractEntity> implements Serializable{
   ...
   protected E myEntity;
  ...     
   abstract public E getMyEntity();
}

public class MyEspecificClass extends MyClass<MyEspecificEntity>{

   private static final long serialVersionUID = 6451465817583035678L;

   @OneToOne(fetch=FetchType.LAZY,cascade=CascadeType.ALL)
   public MyEspecificEntity getMyEntity(){
       return myEntity;
   }
   
}