Pg. 420 - Q.6 of HF book

[Jayanthi Mani]

Given this question:
11. <% java.util.List list=new java.util.ArrayList();
12. list.add("a");
13. list.add("2");
14. list.add("c");
15. request.setAttribute("list",list);
16. request.setAttribute("listIdx","1");
17. %>
18. <%-- insert code here --%>

Which inserted at line 18 are valid and evaluate to c? (Choose all that apply)

A.${list.2}
B.${list[2]}
C.${list.listIdx+1}
D.{list[listIdx+1]}
E.{list['listIdx'+1]}
F.{list[list['listIdx']]}

The answers are given as B,D,F.

Why is 'E' also not considered a correct answer? I don't understand the explanation that has been given. Can anybody please explain why option 'E' is not an answer?

Thanks,
Jayanthi.

[Roger Yates]

'listIdx' with quotes round it is just the string 'listIdx'.
We can assume that list is of type List and so can be accessed using [] with numbers only. So list[1] is fine, and list[someAttributeThatCanConvertToANumber] is also fine. But list["someAttributeThatCanConvertToANumberButWontAsItIsInQuotes"] will not work.

Actually as it stands F also does not work (exception gets thrown for same reason as E).
Here's the error you get for F as it is now:

The EL expression ${list[list['listIdx']]} throws a ServletException
(The "[]" operator was supplied with an index value of type "java.lang.String" to be
applied to a List or array, but that value cannot be converted to an integer.)

I've logged 'F' as an errata, and it's currently in the 'unconfirmed' bucket here:
http://www.oreilly.com/catalog/headservletsjsp/errata/

[Jayanthi Mani]

Thanks for the explanation.That does clarify my doubt quite nicely

Jayanthi.

[Jessica White]

Roger, I so agree with you.
I had quite a difficult time to accept F as a correct answer.

F. ${list[list['listIdx']]}

'listIdx' would be treated as a String, since it has quotes around it, thus it should not be evaluted. At runtime, EL will try to coerce String 'listIdx' to an int, but of course that would not succeed, unless it is a string like '32'. So, I agree with you that F is not a correct answer.

--Jessic