using <jsp:useBean tag without class attribute

i have a confusion in using usebean tag without class attribute, as the example given in head first servlets

n it says that if the person bean must already exists then only it will work.

1. so my question is this that is it possibility that we can make this work because if we bean is already declared in page scope(then it must be declared in the same page ), n then if we use this line in same page it will give an exception of having duplicate bean.

2. n if we declare it in request scope then also in using it on different jsp page it gives exception "java.lang.InstantiationException:bean not found in the scope"

3. but if i declare it in session scope then it is working fine on the next jsp page.

so please solve my above mentioned questions