Eclipse: Why classes created manually aren't recognized?

For example: I'm making an Web project. At some line of one servlet, I put the following line:

ContatoDao dao = new ContatoDao();

So Eclipe complains that ContatoDao can't be found. And it's right; this class is at another package. So, in order to test, I copied contatoDao to the same directory of the present class (also changing it's package to the same package of the present class). But I keep getting this error:

HTTP Status 500 - Servlet execution threw an exception


  (...)


root cause
java.lang.Error: Unresolved compilation problems: 
    ContatoDao cannot be resolved to a type
    ContatoDao cannot be resolved to a type

Which doesn't occurs if I create the same class, at the same place, but using the create class of Eclipe. Why?