This week's book giveaway is in the OO, Patterns, UML and Refactoring forum.
We're giving away four copies of Five Lines of Code and have Christian Clausen on-line!
See this thread for details.
Win a copy of Five Lines of Code this week in the OO, Patterns, UML and Refactoring forum!
  • Post Reply Bookmark Topic Watch Topic
  • New Topic
programming forums Java Mobile Certification Databases Caching Books Engineering Micro Controllers OS Languages Paradigms IDEs Build Tools Frameworks Application Servers Open Source This Site Careers Other all forums
this forum made possible by our volunteer staff, including ...
Marshals:
  • Campbell Ritchie
  • Bear Bibeault
  • Ron McLeod
  • Jeanne Boyarsky
  • Paul Clapham
Sheriffs:
  • Tim Cooke
  • Liutauras Vilda
  • Junilu Lacar
Saloon Keepers:
  • Tim Moores
  • Stephan van Hulst
  • Tim Holloway
  • fred rosenberger
  • salvin francis
Bartenders:
  • Piet Souris
  • Frits Walraven
  • Carey Brown

Doubt about JWeb+ mock exam question

 
Greenhorn
Posts: 16
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Hello,
In jweb+ mock exams, there is one question on EL which is like

Consider the following code appearing in a JSP file:

<%
request.setAttribute("names", new String[]{ "A", "B", "C" } );
request.setAttribute("index", "1");
%>
<h1><!-- insert code here --></h1>
Which of the following statements will print B in inserted in the above JSP page?
Select 3 correct options

The answer listed are:
b ${names[1]}
c ${names.index}
d ${names[index]}

By the way the other options listed for this question are:
a ${names.1}
e ${names.$index}
f ${names[$index]}


Reading HFSJ, I thought ${name.index}, can be used only when the first attribute is a Map or a Bean and the second one after the . is a key in a Map or a property in a Bean. Further, I remember reading that for Array Lists, List etc the [] operator needs to be used.

Am, I misunderstanding some thing?

Thanks a lot
Siva
 
Ranch Hand
Posts: 90
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
You are correct. I tried some coding and proved c is wrong. Here is the error message I got:

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.
 
Jingh Yi
Ranch Hand
Posts: 90
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Can anyone explain to me why option f: ${names[$index]} prints nothing?

Thanks!
 
Ranch Hand
Posts: 152
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Hi Jinghui

The option f is ${names[$index]}
here $index is not in braces {} i guess that is the reason it is not printing
anything

Try ${names[${index}]} I think it will print B again

Catch You Later
Shiva
 
Ranch Hand
Posts: 47
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Hi,

Will the expression ${names["index"]} will print B ?


Thanks and Regards,
Rufus
 
shiva viswanathan
Ranch Hand
Posts: 152
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Hi ,

No , it will not work
This is just plain old java syntax error


${names["index"]}

names["index"] is not a valid java expression since the index of an array
should be integer but here it is string

There is no connection here to EL since there are no ${}
around index
 
J Johny Rufus
Ranch Hand
Posts: 47
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Hi Shiva,

Assuming names is a Map

<%
HashMap map = new HashMap();
map.put("1","first");
request.setAttribute("names", map );
request.setAttribute("index", "1");
%>

Will this work ?
${names["index"]}

Tanks in advance
Rufus
 
shiva viswanathan
Ranch Hand
Posts: 152
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
HI ,


In ${names["index"]} "index" is a string literal so it will not work
However ${names[index]} ie without quotes will work since
we have set the index var in the request

ie ${names[index]} --> ${names["1"]} -------> first

And yeah , i didnt explain properly in my previous post
${names["1"]} is valid in case of EL though not in java
 
J Johny Rufus
Ranch Hand
Posts: 47
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Thanks Shiva
 
Jingh Yi
Ranch Hand
Posts: 90
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Hi Shiva,

I tried your suggestion and it didn't work. My code is listed below:



I got this error:


Do you know why?

Thanks!
Jenny
 
shiva viswanathan
Ranch Hand
Posts: 152
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Hi Jinghui ,

You have tried the wrong expression . If you look at my previous post
the expression i had suggested is ${names[index]}
whereas the expression you tried is ${names[${index}]}

This is because when nesting expressions you need to use only one $ sign
If 2 or more present then the error you got is thrown

Morover even with the first expression i dont think it will work
since you are setting the var in the request scope and trying to access it in the same page (which is not in request scope )

try putting it in the page scope with the first expression i suggested

Thanks
Shiva
 
Jingh Yi
Ranch Hand
Posts: 90
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Thanks, Shiva. ${names[index]} works. And I don't have to put it in page scope since the EL automatically checks request scope when it's not in page scope.
 
Don't get me started about those stupid light bulbs.
    Bookmark Topic Watch Topic
  • New Topic