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uncheked or unsafe operations

 
akashvinay vinaydeo
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hey
while comiling the following code from Head First servlets & JSP page no.82

i am getting following error

BeerExpert.java uses unsafe or unchecked operations
Recompile with -Xlint:unchked for details

please help:
akash.deo@iiitb.net
 
Campbell Ritchie
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Welcome to JavaRanch

That's not an error, but a warning. If you recompile with javac -Xlint:unchecked BeerExpert.java it will tell you what it thinks the problem is.
What it means is that there is a risk of your putting something into the Lists and trying to get it out as a different type, in which case there will be a ClassCastException thrown.
That sort of warning only started appearing when Java5 was introduced in Autumn 2004. It can be obviated by using generics, but that is probably too advanced a topic for the earlier pages of a Head First book. By the way: was that book printed before Autumn 2004?
 
It is sorta covered in the JavaRanch Style Guide.
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