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About the empty constructor

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Ok, Kathy told us 1000000 times that one of the requirements for a bean is to declare an empty constructor...BUT...I remember quite well that more than once we were also suggested not to write this method at all (unless in case of particular reasons) and to leave the constructor to the compiler. Now, I've got on question like the following:

Identify all correct requirements for a CMP entity bean class? [Check all correct answers]

1. The class must be defined as public.
2. The class must define a public constructor that takes no arguments.
3. The class must not be defined as abstract.
4. The class must define the finalize() method.
5. The class must implement, directly or indirectly, the javax.ejb.EntityBean interface.

I replied 1 and 5 (not 2) because I supposed that the entity bean class must NOT define an empty constructor, as the compiler creates one for us. Why this is wrong? (The correct answers were 1,2, 5)
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No 2 is a requirement. So you should have no arg Constructor, but how it got there is not the question. Whether compilers puts it or you write it, it doesn't matter, you should have it.

So you should select 2 as an answer.
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