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useBean standard action.

 
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Hi,

In the useBean standard action we can use class and type attributes in combination.

Is there is any specific case where you should use both in one useBean standrad action.

Thanks
 
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You must use the class & type attribute together if the bean tht u r referring to is not available in the said scope already. It will throw an IllegalStateException.
 
Narendra Dhande
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Hi Jayashree,

I think this can be done without the type attribute. Only class attribute is sufficient.

Thanks
 
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In the useBean standard action we can use class and type attributes in combination.



Yes u can use both class & type.


Is there is any specific case where you should use both in one useBean standrad action.



This is clearly explained in SCWCD exam study kit.If u dont have one here is a simple example.

interface animal{}

class dog implements animal{}

class cat implements animal{}

In java we get used to use the stmt something like this :

animal a = new dog();

What is it implying?.Parent reference is pointing to child object.In the same way we can use it for usebean declaration in JSP also.

<jsp:usebean id="pet" class="dog" type="animal" scope="session"/>

The above declaration is equivalent for the following stmts

animal pet = (animal)session.getAttribute("pet");

if(animal==null){

pet = new dog();

}

hth..

Regards,
Priya.
 
Narendra Dhande
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Hi Priya



<jsp:usebean id="pet" class="dog" type="animal" scope="session"/>



I want to say, here I know I am using the the dog class. and it is subclass of animal. So, is there is any need to specify type="animal". If I pass other subclass of the animal (cat). This is error due to the class="dog".
so there is no need to specify the type="animal" attribute. I think it is reductant. I want to know, there is any particular case, where it is necessary to specify both please tell me, because I personaly think there is no need to specify both in the useBean.

Thanks
 
Priya Jothi
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Ok u r asking for when/why it is used rather than how it used..am i right?.

Considering the same example u can create dog instance in 2 ways..

dog d = new dog();

or

animal a = new dog();

These are the 2 possible ways to create a dog instance..nothing can state u should use the one over the other..coz that is upto the designer who design the java class / JSP.How u r goin to make use of that bean object in ur JSP is left to you.

Coming to ur doubt in case u dont specify type attribute for the usebean declaration instantiation will be the first scenario..else if u specify type attribute as "animal" it'll be of the second one.Both are legal!!

Regards,
Priya.
 
Narendra Dhande
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Thanks Priya, I got the clue.
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