This might sound stupid to you, but why do I need to define an empty constructor in my @Entitys?

Every tutorial I saw said : every entity needs an empty constructor.

But Java always give you a default invisible empty constructor (if you don't redefine one).

Let me clarify.. What I understood by "need" was write.

Meaning: always write an empty constructor in your entity.

example:

@Entity
public class MyEntity implements Serializable {

   @Id
   private String str;

   public MyEntity(){}

   //here getter and setter
}

But Java always gives you this empty constructor when you don't redefine it (write an other one with parameters).

In this case writing this empty constructor seems useless.