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What does it mean ?

Edisandro Bessa
Ranch Hand

Joined: Jan 19, 2006
Posts: 584
Hi guys,

What does the following affirmation mean ?

"All instances of a generic class have the same runtime class, regardless of their actual type parameters. So it is not meaningful to use the instanceof operator to check if an object is the instance of a particular invocation of a generic type."

Could you please explain by using code ?

Thanks


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Barry Gaunt
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Joined: Aug 03, 2002
Posts: 7729
An example: ArrayList<String> list1, ArrayList<List> list2, ArrayList<Integer> list3, ArrayList<Double> list4 are all reduced to the raw type ArrayList at runtime. So you can only ask if list1 instanceof ArrayList, or list2 instanceof ArrayList, and so on. You cannot ask if list1 instanceof ArrayList<String> or list2 instanceof ArrayList<List>


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Edisandro Bessa
Ranch Hand

Joined: Jan 19, 2006
Posts: 584
*Bump*. Now I see. Now it's clear.

Thank you Sir.
[ April 18, 2006: Message edited by: Edisandro Bessa ]
 
It is sorta covered in the JavaRanch Style Guide.
 
subject: What does it mean ?
 
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